Linguistically, the word Tawheed توحيد, in Arabic, means unification (to make something one). Islamically, it is in reference to Allaah being singled out alone, in all that is particular to Him. The opposite of Tawheed is 'Shirk' which is to associate partners with Allaah by giving (or attributing) that which is exclusively His to others . It comes from the Arabic verb (wahhada) وحد which itself means to unite, unify or consolidate. However, when the term Tawheed is used in reference to Allaah (i.e. Tawheedullaah), it means the realizing and maintaining of Allaah's unity in all of man's actions which directly or indirectly relate to Him. It is the belief that Allaah is One, without partner in His dominion and His actions (Ruboobeeyah), One without similitude in His essence and attributes (Asmaa wa Sifaat), and One without rival in His divinity and in worship (Ulooheeyah/'Ebaadah). These three aspects form the basis for the categories into which the science of Tawheed has been traditionally divided. The three overlap and are inseparable to such a degree that whoever omits any one aspect has failed to complete the requirements of Tawheed. The omission of any of the above mentioned aspects of Tawheed is referred to as "Shirk" (lit. sharing); the association of partners with Allaah, which, in Islamic terms, is in fact idolatry 
Traditionally, Tawheed has been divided into three categories which help us to understand why Allaah alone deserves to be singled out for worship. The division of Tawheed into these three categories is something which was not done by Prophet Muhammad, sallallaahu alayhi wa sallam, or any of his companions, may Allaah be pleased with them. So, is this Bid'ah (i.e., something new that has been introduced into the religion)? The answer to this is no, because we find that the basis of these three categories are to be found in the verses of the Quran, Hadeeth [authenticated Prophetic reports] of the Prophet, sallallaahu alayhi wa sallam, and the statements of his companions 
The necessity for dividing up Tawheed into three categories first came about during the early days of Islam. After the death of the Prophet, sallallaahu alayhi wa sallam, Islam spread like wildfire and before long the empires of Africa, Byzantium, Persia and India all fell under Muslim rule. Many people from these areas became Muslims. However some of these converts to Islam also carried with them some of their old pagan beliefs. This caused much confusion amongst people, and the simple belief of Islam which the people had accepted started to become clouded. The task of opposing these new thoughts and ideas which were becoming prevalent, fell upon the shoulders of the Muslim scholars, who rose to meet this challenge intellectually. Amongst the first people to divide Tawheed into three categories was the famous scholar of Iraq, Abu Haneefah, may Allaah have mercy upon him.
From early times the scholars have categorized the rulings of sharee’ah. This has only been done to make it easier to understand the texts and rulings of sharee’ah, especially as time goes by and knowledge of Arabic language becomes weaker and the language gets mixed with foreign language
The scholars thought it wise to set out principles, issues and categories to make it easier to understand. There is nothing wrong with this, in fact it is a good thing because it makes knowledge more accessible to the Muslims. Al-Shaafa’i set out the principles of fiqh and his categorization was well-received and was followed by the scholars of usool who wrote commentaries on what he said and added to it. This was done in all branches of Islamic knowledge such as tajweed (recitation of Qur’aan), Qur’aan and others, including Tawheed.
Before mentioning what these three categories are, it has to be stressed that the concept of Tawheed is in no way similar to the Christian concept of trinity. The division of Tawheed does not divide Allaah up into three separate parts (as does trinity), but rather it helps us to understand as to how our Creator is Unique and Alone in being singled out for worship and reverence.
 "The Fundamentals of Tawheed (Islamic Monotheism)" By Bilal Philips
1- The Unity of Allaah's Lordship
This first category of Tawheed is known as Tawheed-Ar Ruboobiyyah or the unity of Allaah's Lordship. Through this we understand that it is Allaah Who Alone created the universe, which is why one of His divine names is Al-Khaaliq (the Creator). Through this we know that it is Allaah Alone Who controls the universe and allows things to happen. This is why Allaah refers to Himself in the Quran as Al-Malik (The Sovereign). Hence, when something happens, it only happens with the permission of Allaah, as stated in the Quranic verse (which means): "And no calamity strikes except with the permission of Allaah" [Quran 64:11]
This category is based on the fundamental concept that Allaah alone caused all things to exist when there was nothing; He sustains and maintains creation without any need from it or for it; and He is the sole Lord of the universe and its inhabitants without any real challenge to His sovereignty. In Arabic the word used to describe this creator-sustainer quality is Ruboobeeyah which is derived from the root "Rabb" (Lord). According to this category, since God is the only real power in existence, it is He who gave all things the power to move and to change. Nothing happens in creation except what He allows to happen. In recognition of this reality, Prophet Muhammad (saws) used to often repeat the exclamatory phrase "La hawla wa laa quwwata illaa billaah" (There is no movement nor power except by Allaah's will).
The Prophet, sallallaahu alayhi wa sallam, further elaborated on this concept of Allaah's control over the universe by saying: "Be aware that if the whole of mankind gathered together in order to do something to help you they would only be able to do something for you which Allaah had already written for you. Likewise, if the whole of mankind gathered together to harm you, they would only be able to do something to harm you which Allaah had already written to happen to you". [At-Tirmithi] 
Thus, what man conceives as good fortune and misfortune are merely events predestined by Allaah as part of the tests of this life. The incidents follow patterns set only by Allaah. Allaah has said in the Qur'aan: "O Believers! Surely there Is In your wives and children an enemy for you, so beware of them." [ At-Taghabun 64:14]
That is, within the good things of this life there are severe tests of one's faith in God. Likewise, in the terrible events of life there lies test as is mentioned in the verse: "Surely We will test you with fear, hunger, loss of wealth and life and the fruits of your work, so give glad tidings to those who are patient." [Al-Baqarah 2:155]
Sometimes the patterns are recognizable, as in the case of cause and effect relationships, and sometimes they are not, as in the case when apparently good results come from evil means or bad results from good means. God has explained that the wisdom behind these apparent irregularities is often beyond man's immediate comprehension due to his limited scope of knowledge. "Perhaps you may dislike something which is really good for you or like something bad for you, but Allaah knows (what is best for you), and you do not." [Al-Baqarah 2:216]
Apparently evil events in human lives sometimes turn out to be for the best and apparently good things which people desire turn out to be harmful. Consequently, man's realm of influence in the course of events which make up his life is limited to the mental choice between options presented to him and not the actual results of his choice. In other words "man proposes and God disposes". Apparent "good fortune" and "misfortune" are both from Allaah and can not be caused by good-luck charms such as rabbit's feet, four-leaf clovers, wishbones, lucky numbers, zodiacal signs, etc., or by omens of bad luck like Friday the thirteenth, breaking mirrors, black cats, etc.
In fact, the belief in charms and omens is a manifestation of the grave sin of Shirk (association) in this form of Tawheed. 'Uqbah, one of the companions of the Prophet (peace be upon him), reported that once a group of men approached Allaah's messenger to give their allegiance to him, and he accepted the oath from nine of them but refused to accept it from one. When they asked him why he refused their companion's oath, he replied, "Verily, he is wearing an amulet" The man who was wearing the amulet put his hand in his cloak, pulled the amulet off and broke it then made the oath. The Prophet (peace be upon him) then said, "Whoever wears an amulet has committed Shirk."
As for using the Qur'aan like a charm or amulet by wearing or carrying Qur'anic verses on chains or in pouches to ward off evil or to bring good fortune, there is little difference between such practices and those of the pagans. Neither the Prophet (peace be upon him) nor his Companions used the Qur'aan in this fashion, and the Prophet (peace be upon him) said, "Whoever innovates in Islaam something which does not belong to it will have it rejected."
It is true that the Qur'anic chapters, an-Naas and al-Falaq, were revealed specifically for exorcism (that is, for removing evil spells), but the Prophet (peace be upon him) demonstrated the proper method by which they should be used. On an occasion when a spell had been cast on him, he told 'Alee ibn Abee Taalib to recite the two chapters verse by verse and when he became ill he used to recite them on himself. He did not write them down and hang them around his neck, tie them on his arm or around his waist, nor did he tell others to do so. 
We know that another name, which Allaah chooses to call Himself by, is Ar-Razzaaq (the Sustainer). It is Allaah who provides us with our food, shelter, clothing, families and friends. When our crops seem to be dying and there is not a cloud in sight, it is Allaah Who sends down His rain from the skies and sustains us. Allaah Says (what means): "Allaah is the Creator of all things and He is, over all things, Disposer of affairs." [Quran 39:62]
From this you would expect that people would turn back to Allaah for good or bad fortune. However, this is not the case. Today we find some people relying on all kinds of good luck charms, which they believe will bring them good fortune and ward off evil.
These practices have absolutely no basis whatsoever in Islam, but rather the Prophet, sallallaahu alayhi wa sallam, warned us by saying: "Whosoever brings something new into Islam (which does not belong to it) will have it rejected". [Al-Bukhaari]
 "The Fundamentals of Tawheed (Islamic Monotheism)" By Bilal Philips
2- The Unity of Allaah's names and Attributes
This category of Tawheed is known as Tawheed Al-Asmaa' Was-Siffaat or the unity of Allaah's Names and Attributes. Allaah Says in the Quran (what means): "Allaah — there is no deity except Him. To Him belong the best names." [Quran 20:8]
This category of Tawheed helps us to understand Who our Creator is through His Names and Attributes. Through His Names and Attributes we know that Allaah is far beyond our imagination and bears no resemblance to human beings. In fact, it is this principle which makes Islam unique from all the other religions on the face of this earth. Allaah Says (what means): "There is nothing like unto Him and He is the Hearing, the Seeing." [Quran 42:11]
This category of Tawheed has five main aspects:
1. For the unity of Allaah's names and attributes to be maintained in the first aspect, Allaah must be referred to according to how He and His Prophet (peace be upon him) have described Him without explaining away His names and attributes by giving them meanings other than their obvious meanings. For example, Allaah in the Qur'aan says He gets angry with the disbelievers and the hypocrites. He says:
"That He may punish the hypocrites, men and women, and the pagans men and women, who have an evil opinion of Allaah. A circle of evil is around them; Allaah is angry with them, curses them and has prepared for them an evil end."[Al Quran 48:6]
Thus, anger is one of God's attributes. It is incorrect to say that His anger must mean His punishment since anger is a sign of weakness in man and, as such, not befitting of Allaah. What Allaah has stated should be accepted with the qualification that His anger is not like human anger, based on Allaah's statement, "There is nothing like him" [Al Quran 42:11]
The process of so-called "rational" interpretation when taken to its logical conclusion results in the denial of God's very existence. For, Allaah describes Himself as living and man lives, therefore, according to the rationalist argument, God is neither living nor existing. The fact is that the similarity between God's attributes and those of mankind is only in name and not in degree. When attributes are used in reference to God, they are to be taken in the absolute sense, free from human deficiencies.
2. The second aspect of Tawheed al-Asmaa was-Sifaat involves referring to Allaah as He has referred to Himself without giving Him any new names or attributes. For example, Allaah may not be given the name al-Ghaadib (the Angry one), in spite of the fact that He has said that He gets angry, because neither Allaah nor His messenger has used this name. This may seem to be a very fine point, but it must be maintained in order to prevent the false description of God. That is, finite man is in no position to define the infinite Lord of creation.
3. In the third aspect of Tawheed al-Asmaa was-Sifaat Allaah is referred to without giving Him the attributes of His creation. For example, it is claimed in the Bible and Torah that Allaah spent the first six days creating the universe then slept on the seventh. [Genesis 2:2] (Holy Bible, Revised Standard Version (Nelson, 1951), p.2)
For this reason, Jews and Christians take either Saturday or Sunday as a day of rest in which work is looked at as a sin. Such a claim assigns to God the attributes of His creation. It is man who tires after heavy work and needs sleep to recuperate. In contrast Allaah says explicitly in the Qur'aan, "No tiredness overcomes Him nor sleep..." (Al Quran 2:255).
Elsewhere in the Bible and Torah, God is portrayed as repenting for His bad thoughts in the same way that humans do when they realize their errors. [Exodus 32:14] (Holy Bible, Revised Standard Version),
Similarly the claim that God is a spirit or has a spirit completely ruins this area of Tawheed. Allaah does not refer to Himself as a spirit anywhere in the Qur'aan nor does His Prophet (saws) express anything of that nature in Hadeeth. In fact, Allaah refers to the spirit as part of His creation. Allaah clearly states that in the following verse: "They ask you (Muhammad) about the spirit. Tell (them) that the spirit (exists) by my Lord's command" (Al Quran 17:85).
The key principle which should be followed when dealing with Allaah's attributes is the Qur'anic formula,
"There is nothing like Him and He is hearer and seer of all." [Al Quran 42-11]
The attributes of hearing and seeing are among human attributes, but when they are attributed to The Divine Being they are without comparison in their perfection. However, when these attributes are associated with men they necessitate ear and eye apparatuses which can not be attributed to God.
What man knows about the Creator is only what little He has revealed to him through His prophets. Therefore, man is obliged to stay within these narrow limits. When man gives free rein to his intellect in describing God, he is liable to fall into errors by assigning to Allaah the attributes of His creation.
In their love of pictorial representations, Christians have painted, carved and molded innumerable human likenesses and called them images of God. These have served to pave the way for the acceptance of Jesus' divinity among the masses. Once they accepted the conception of the Creator as being like a human being, accepting Jesus as God presented no real problem.
4. The fourth aspect of Tawheed al-Asmaa was-Sifaat requires that man not be given the attributes of Allaah. For example, in the New Testament Paul takes the figure of Melchizedek, king of Salem, from the Torah (Genesis 14:18-20) and gives both him and Jesus the divine attribute of having no beginning or end,
"1 For this Melchizedek, king of Salem, priest of the most high God, met Abraham returning from the slaughter of the kings and blessed him,2 and to him Abraham apportioned a tenth part of everything. He is first, by translation of his name, king of righteousness, and then he is also king of Salem, that is, king of peace.3 He is without father or mother or genealogy, and has neither beginning of days nor end of life, but resembling the son of God he continues a priest forever." [Hebrews 7:1-3] (Holy Bible, Revised Standard Version)
"5 So also Christ did not exalt himself to be made a high priest, but was appointed by him who said to him, 'Thou art my son, today I have begotten thee'; 6 as he says also in another place, 'Thou art a priest for ever, after the order of Melchizedek'. [Hebrews, 5:5-6] (Holy Bible, Revised Standard Version).
Most Shi'ite sects (with the exception of the Zaidites of Yemen) have given their "Imaams" divine attributes of absolute infallibility knowledge of the past, the future and the unseen, the ability to change destiny  and control over the atoms of creation. In so doing they set up rivals who share God's unique attributes and who, in fact, become gods besides Allaah.
5. Maintaining the unity of Allaah's names also means that Allaah's names in the definite form cannot be given to His creation unless preceded by the prefix 'Abd meaning "slave of" or "servant of'. Many of the Divine names in their indefinite form like Ra'oof and Raheem are allowable names for men because Allaah has used some of them in their indefinite forms to refer to the Prophet (peace be upon him):
"A messenger has come to you from among yourselves to whom anything which burdens you is grievous. He is full of concern for you and is full of pity (Ra'oof) and full of mercy (Raheem)".[Al Quran 9:128]
But ar-Ra'oof (the One Most Full of Pity) and ar-Raheem (the Most Merciful) can only be used to refer to men if they are preceded by 'Abd as in 'Abdur-Ra'oof or 'Abdur-Raheem, since in the definite form they represent a level of perfection which only belongs to God. Similarly, names like 'Abdur-Rasool (slave of the messenger), 'Abdun-Nabee (slave of the Prophet), 'Abdul-Husayn (slave of Husayn), etc.,where people name themselves slaves to other than Allaah are also forbidden. Based on this principle, the Prophet (saws) forbade Muslims from referring to those put under their charge as 'Abdee (my slave) or Amatee (my slave girl). (Sunan Abu Dawud, (English Trans.), vol.3, pp. 1385-86, no.4957).
 Muhammad Rida al-Muzaffar states in his book Faith of Shi'a Islam, (U.S.A.: Muhammadi Trust of Great Britain and Northern Ireland, 2nd ed. 1983): "We believe that, like the prophet, an Imam must be Infallible, that is to say incapable of making errors or doing wrong, either Inwardly or outwardly, from his birth to his death, either intentionally or unintentionally, because the Imams are the preservers of Islam and it is under their protection." (p.32). See also Islam, (Teheran: A Group of Muslim Brothers, 1973), p.35, by Sayed Saeed Akhtar Rizvi.
 AI-Muzaffar further states: "We maintain that the powers of the Imams to receive inspiration has reached the highest degree of excellence, and we say that it is a Divinely - given power. By this means the Imam is able to understand information about anything, anywhere, and at any time, and he understands by means of this Divinely - given power at once, without recourse to methodological reasoning or guidance from a teacher.
 Al-Khomeini states: "Certainly the Imam has a dignified station, a lofty rank, a creational caliphate, and sovereignty and mastery over all atoms of creation." (Aayatullah Musavi al-Khomeini, al-Hukoomah al-Islaameeyah, (Beirut: at-Talee'ah Press; Arabic ed., 1979), p.52).
"The Fundamentals of Tawheed (Islamic Monotheism)" By Bilal Philips
In spite of the wide implications of the first two categories of Tawheed, firm belief in them alone is not sufficient to fulfill the Islamic requirements of Tawheed. Tawheed ar-Ruboobeeyah and Tawheed al-Asmaa was-Sifaat must be accompanied by their complement, Tawheed al-'Ebaadah, in order for Tawheed to be considered complete according to Islaam. This point is substantiated by the fact that Allaah Himself has related in clear terms that the Mushrikoon (idolators) of the Prophet's time confirmed many aspects of the first two forms of Tawheed. In the Qur'aan Allaah tells the Prophet (saws) to say to the pagans:
"Say: 'Who is it that gives you all sustenance from the sky and earth, governs sight and hearing, brings forth life from dead (matter) and death from the living, and plans the affairs of man?' They will all say 'Allaah'." [Al Quran 10:31]
"If you asked them who created them, they would surely say, 'Allaah' " [Al Quran 43:87]
"If you asked them who brings down water from the sky and with it brings the earth to life after its death? They will most certainly say, 'Allaah'." [Al Quran 29:63] 
There is nothing to prevent a person from calling directly upon Allaah and asking for His help and forgiveness. Unfortunately, this is violated by most of mankind who believe that other men can intercede for them and even grant them forgiveness because of their apparent special status! An example of this is the Catholic religion which holds that the celibate priests are purer than normal people. This allows for them to then hear the confessions of people's sins and subsequently grant them forgiveness. It is this kind of behaviour which takes a person away from the worship of Allaah to the worship of man. 
The pagan Makkans all knew that Allaah was their creator, sustainer, their Lord and Master yet that knowledge did not make them Muslims according to God. In fact, Allaah said:
"Most of them do not believe in Allaah except while joining partners to Him."38
Mujaahid's commentary on this verse was as follows: "Their belief in Allaah represented by their statement, 'Allaah created us, provides for us and takes our lives', did not stop them from worshipping other gods along with Allaah."Collected by Ibn Jareer at-Tabaree
From the previously mentioned verses, it is clear that the Kuffaar (disbelievers) knew of Allaah's sovereignty, dominion and power. In fact, they used to faithfully devote various types of worship to Him like Hajj, charity, animal sacrifices, vows and even prayers in times of dire necessity and calamity. They even used to claim that they were following the religion of Abraham. Because of that claim, Allaah revealed the verse:
"Abraham was not a Jew nor was he a Christian, but (he) was a true Muslim and not among those who joined partners with Allaah." [Al Quran 3:67]
Some pagan Makkans even believed in the Resurrection and the Judgement and others in predestination (Qadar). Ample evidence of their belief can be found in pre-Islamic poetry. For example, the poet Zuhayr was reported to have said:
"It is either delayed, placed in a book and saved for the Day of Judgement or hastened and avenged."
'Antarah was quoted as saying:
"O 'Ebil to where will you run from death, if my Lord in the sky has destined it?" 
In spite of the Makkans' confessions of Tawheed and their knowledge of Allaah, Allaah classified them as disbelievers (Kuffaar) and pagans (Mushrikoon) simply because they worshipped other gods along with their worship of Allaah.
Consequently, the most important aspect of Tawheed is that of Tawheed al-'Ebaadah, maintaining the unity of Allaah's worship. All forms of worship must be directed only to Allaah because He alone deserves worship, and it is He alone who can grant benefit to man as a result of His worship. Furthermore, there is no need for any form of intercessor or intermediary between man and God. Allaah emphasized the importance of directing worship to Him alone by pointing out that this was the main purpose of man's creation and the essence of the message brought by all the prophets. Allaah says:
"I did not create the Jinn and Mankind except for My worship." [Al Quran 51:56]
"Verily, We have sent to every nation a messenger (saying), 'Worship Allaah and avoid false gods'." [Al Quran 16:36]
Understanding the purpose of creation in a complete sense is beyond man's innate abilities. Man is a finite created being and can not reasonably hope to fully comprehend the actions of the infinite Creator. Hence, God made it a part of man's nature to worship Him, and He sent prophets and books of divine revelation to clarify the aspect of the purpose of creation which was within man's mental ability to grasp. That purpose is, as was previously mentioned: the worship of God ('Ebaadah) and the main message of the prophets was to worship God alone, Tawheed al-'Ebaadah. Consequently, the gravest sin is Shirk, the worship of others instead of Allaah or along with Allaah. In Soorah al-Faatihah, which every Muslim is required to recite in his or her prayers at least seventeen times daily, verse four reads, "You alone do we worship and from You alone do we seek help". A clear statement that all forms of worship should only be directed to the One who can respond, Allaah. The Prophet Muhammad (saws) confirmed the concept of unity of worship saying, "If you ask in prayer ask only Allaah, and if you seek help, seek it only from Allaah." [Reported by Ibn 'Abbaas and collected by at-Tirmidhee. See An-Nawawi's Forty Hadith, (English Trans.), p.68]
The absence of any need for intercession is further emphasized by the many verses indicating His closeness to man. For example:
"When My servants ask you (O Muhammad) about Me (tell them), 'Verily I am close (to them), I listen to the prayer of every one who calls on Me. So let them respond to Me and believe In Me in order that they may he guided aright." [Al Quran 2:186]
"It is We who created man and We know what his soul whispers to him, for We are nearer to him than his jugular vein." [Al Quran 50:16]
The confirmation of Tawheed al-'Ebaadah conversely necessitates the denial of all forms of intercession or association of partners with Allaah. If someone prays to the dead seeking their influence on the lives of the living or the souls of those who have passed away, they have associated a partner with Allaah, because worship is being shared between Allaah and His creation. The Prophet Muhammad (saws) said, in no uncertain terms, "Prayer (du'aa) is worship." Sunan Abu Dawud, vol.1, p.387, no.1474.
Allaah, Most Great and Glorious, said:
'Do not worship besides Allaah that which can not help or harm you." [Al Quran 21:66]
"Those on whom you call besides Allaah are only slaves like yourselves." [Al Quran 7:194]
If someone prays to the Prophet (saws), to so-called saints, Jinns or angels asking for help or asking them to request help from Allaah for them, they have also committed Shirk. The concept of "Ghaus-i-Azam" (al-Ghawth al-A'dHam), a title given by the ignorant to 'Abdul-Qaadir al-Jeelaanee, is also an expression of Shirk in this form of Tawheed. The title literally means "the greatest source of rescue; the one most able to save someone from danger" and such a description only belongs to Allaah. When misfortune occurs, some people call on 'Abdul-Qaadir by this title seeking his aid and protection even though Allaah has already said:
"If Allaah allows harm to befall you none can. remove it except Him." [Al Quran 6:17]
According to the Qur'aan, when the Makkans were questioned about directing their prayers to their idols, they answered: "We only worship them so that they may bring us closer to Allaah." [Al Quran 39:3 ]
The idols were only used as intermediaries yet Allaah called them pagans for their practice. Those among Muslims who insist on praying to other than Allaah would do well to reflect on this fact.
Christians, influenced by the teachings of Saul from Tarsus (later called Paul), deified Prophet Jesus and directed their prayer to him and his mother. The Catholics among Christians have saints for every occasion to whom they direct their prayers in the belief that these saints can directly influence the affairs of this world. The Catholics also use their priests as intercessors between themselves and Allaah in the mistaken belief that the priests are closer to Allaah due to their celibacy and piety, and thus more likely to be listened to by Allaah. Most Shi'ite sects have devoted certain days of the week and hours of the day for prayer to 'Alee, Faatimah, Hasan and Husayn54 due to their distorted belief in intercession.
Worship ('Ebaadah) in the Islamic view, includes more than just fasting, paying Zakaah, Hajj and animal sacrifices. It includes emotions like love, trust, and fear, all of which have degrees which should only be directed to God. Allaah has addressed these emotions and warned against excesses in them as follows:
"There are among men those who take (for worship) others besides Allaah as equals to Him. They love them as they should only love Allaah. But those who believe have a much greater love of Allaah..." [Al Quran 2:165]
"Will you not fight people who broke their oaths, plotted to expel the messenger and were the first to (attack) you? Do you fear them? Allaah has more right to be feared if you are truly believers." [Al Quran 9:13]
"Put your trust in Allaah if you are truly believers." [Al Quran 5:23]
Since the term 'Ebaadah means total obedience and Allaah is considered the ultimate Lawgiver, the implementation of secular legal systems not based on divine law (Sharee'ah) is an act of disbelief in the divine law and belief in the correctness of such systems, such a belief constitutes a form of worshipping other than Allaah (Shirk). Allaah said in the Qur'aan:
"Those who do not rule by what Allaah has revealed are disbelievers (Kaafiroon). " [Al Quran 5:44]
On one occasion, the Prophet's companion 'Adee ibn Haatim, who was a convert from Christianity, heard the Prophet (saws) recite the Qur'anic verse, "They have taken their rabbis and monks as lords besides Allaah," [Al Quran 9:31] so he said: 'Surely we did not worship them,' The Prophet (saws) turned to him and said 'Did they not make forbidden (Haraam) what Allaah had made allowable (Halaal) , and you all made it Haraam, and did they not make Halaal what Allaah made Haraam  and you all made it Halaal?' He replied, 'We certainly did.' The Prophet (saws) then said, 'That was how you worshipped them'." [Collected by at-Tirmidhee]
Hence, a significant part of Tawheed al-'Ebaadah involves the implementation of Sharee'ah, especially in lands where Muslims form the majority of the population. Divine law has to be re-introduced in the many so-called Muslim countries where governments now rule according to imported capitalist or communist constitutions, and Islamic law is either totally extinct or relegated to a few areas of minor importance. Likewise, Muslim countries, where Islamic law is on the books but secular laws are in force, have also to be brought in line with the Sharee'ah as it pertains to all aspects of life. The acceptance of non-Islamic rule in place of Sharee'ah in Muslim lands is Shirk and an act of Kufr. Those in a position to change it must do so, while those unable to do so must speak out against the rule of Kufr and call for the implementation of Sharee'ah. If even this becomes impossible, un-Islamic government must be sincerely hated and despised for the pleasure of God and the upholding of Tawheed.
As Muslims, we too should be careful of this, because it seems that many of our brothers and sisters are indulging in this kind of evil and are not even aware of it. How many Muslims are there today who call upon others besides Allaah? We find that in some countries, there are millions of Muslims who go to the graves of 'saints' and ask them for children, wealth, fame and more sadly, forgiveness. What makes this more ironic is the fact that many of these Muslims pray five times a day, and in every Rak'ah (unit) of their prayer they say the following to their Creator: "It is You we worship and You we ask for help." [Quran 1:4]
Learning about the Tawheed of Allaah is the most important thing for the whole of humanity. For if we learn how to trust and worship our Creator with sincerity, then -and only then- will we escape from the slavery and captivity of this life. It is by worshipping Allaah alone does a man achieve true peace and success.
3] Mujaahid ibn Jubayr al-Makkee (642-722) was Ibn 'Abbaas' most outstanding student. The narrations of his Tafseer (commentary) of the Qur'aan has been compiled by 'Abdur-Rahmaan at-Taahir and published in two volumes under the title, Tafseer Mujaahid, (Islamabad: Majma' al-Buhooth).
4] Quoted in Sulaymaan ibn 'Abdul-Wahhaab's Tayseer al-'Azeez al-Hameed, (Beirut: al-Maktab al-Islaamee, 2nd., 1970), p.34.
5] Abdul-Qaadir (1077-1166) was a principal of a school of Hanbalite Law and a Ribaat (monastery) in Baghdad. His Sermons (collected in al-Fat-h ar-Rabbaane, Cairo 1302) were strictly orthodox with some, mystic interpretations of the Qur'aan. Ibn 'Arabee (born 1165) declared him the Qutb of his time and stated that he had a rank which placed him above all beings except God. 'Alee ibn Yousuf ash-Shattanawfee (d. 1314 CE) wrote a book called Bahjat al-Asraar (Cairo, 1304) in which he attributed many miracles to 'Abdul-Qaadir. The Qaadireeyah Sufi order is named after him and its spiritual exercises and regulations traced back to him. (Shorter Encyclopedia of Islam, pp.5-7 and 202-205).
6] Christian clergy made Haraam the marrying of more than one wife and the marrying of first cousins. Roman Catholicism forbade priests from marrying and forbade divorce in general.
"The Fundamentals of Tawheed (Islamic Monotheism)" By Bilal Philips