An Introduction to Islamic Monotheism
There are two Arabic words that are important to know for a discussion of Islamic monotheism. These are tawhid and shirk. Tawhid means "declaring God one", while shirk means "associating partners with God". Thus tawhid is monotheism while shirk is polytheism or idolatry.
The Islamic scholars have defined three aspects to tawhid, each of which has several types of shirk that negate it. Each of these will be discussed in turn.
As explained above, tawhid means "declaring God one." Rububiyya is an Arabic word that is difficult to translate into English. It carries the senses of creating, sustaining, cultivating, and cherishing. A word from the same root is tarbiya, which describes how parents bring up their children, succoring them and drawing out their full nature. Another word from the same root is rabbani which is used in the Quran to refer to teachers and other religious leaders, who supplement parents in providing education and moral guidance to fully develop the child's character. A third word from the same root is Rabb, which is one of God's titles. The Quran tells us that God is the Rabb of all the worlds and of everything in them. Thus rububiyya refers to God as Creator and Sustainer.
Another way of saying this is that rububiyya is a way of referring to God by His functions as God. Tawhid ar-rububiyya thus means declaring that there is only One who holds these divine functions of creating and sustaining the universe. There are two kinds of shirk that negate this, which are polytheism and atheism. Polytheism says that there are many gods who are responsible for creating and sustaining the universe, while atheism says that there is no Creator or Sustainer at all.
Tawhid al-Asma wa as-Sifat
The phrase al-asma wa as-sifat means "the names and the attributes". Thus tawhid al-asma wa as-sifat means "declaring God one in His names and attributes". The names and attributes in question are the famous 99 names. These include The Real (al-Haqq), The Alive (al-Hayy), The Powerful (al-Qawiyy), The Good (al-Barr), and other names such as The Most Gentle (ar-Rahman) and The Mighty (al-Aziz), and many others. A full discussion of the 99 names is beyond the scope of this essay; the point is that these are all qualities that God has. He is Absolute Reality, Absolute Life, Absolute Power, Absolute Good, and so on. Moreover, He is the only being who possesses these or any other qualities in and of Himself. Any reality, life, power, goodness, or other qualities that we have are completely contingent on Him. He gave them to us, and if He willed, He could take them away. And our reality is mixed with non-reality in comparison to God, our life is mixed with death, our power is mixed with incapability, and our goodness is mixed with evil. The Quran tells us about God, "Nothing is like Him" (Surah ash-Shura verse 11) and "There is nothing comparable to Him" (Surah Ikhlas verse 4). No created thing can ever match God in any of His qualities.
And this is the key to understanding tawhid al-asma wa as-sifat. There are two kinds of shirk that negate it, which are the deification of human beings and the humanization of God. The deification of human beings is to say that a human being, a created thing, matches the Absolute Reality (God) in any way. The humanization of God is to impute any non-reality, death, incapability, evil, or the opposite of any of His qualities to God.
The most obvious example of a shirk that negates tawhid al-asma wa as-sifat is the deification of Jesus (peace be upon him). How could Jesus, a human being, be equal to God in any way? How could God, the Absolute Reality, be equal to a human being in any way? This is why Muslims believe that Christianity has fallen short of monotheism.
Another way of expressing tawhid al-asma wa as-sifat is to say that it is possible to recognize only one God as Creator and Sustainer (tawhid ar-rububiyya) but to have the wrong picture of Him. In order to be truly monotheistic, you have to have the right picture of God, and that is what tawhid al-asma wa as-sifat is about. Otherwise you end up worshiping a deified human being or a "micro-god" with human attributes not God.
Ibada is an Arabic word meaning "service" or "worship". Thus, tawhid al-ibada means "declaring God one through our service". There are two kinds of shirk that negate this, which are "outward shirk" and "hidden shirk".
Outward shirk involves offering outward forms of worship to other than God, for instance, praying to Zeus or Shiva (or to Jesus, for that matter), or intending actions in their name, or obeying their commandments instead of God's. This is obviously polytheism or idolatry.
Hidden shirk is basically hypocrisy or "showing off". The Quran says "Have you seen him who takes caprice as his god?" (Surah al-Furqan verse 43). Outwardly, the person appears to be pious and monotheistic, but in his heart, it is his caprices he serves, not God, because those are what he obeys.
Thus, tawhid al-ibada has two aspects. One is to offer the outward forms of worship to God alone, and the other is to have a pure and sincere intention in the heart for God alone.
When we look at the three types of tawhid, we can see that the outward tawhid al-ibada refers to our actions, while tawhid ar-rububiyya and tawhid al-asma wa as-sifat refer to our knowledge and understanding, and the inner tawhid al-ibada refers to our motivations.
In other words, in order to be truly monotheistic, you must not only worship God alone in your prayer (outward tawhid al-ibada) but you must have the correct knowledge (tawhid ar-rububiyya), the correct understanding (tawhid al-asma wa as-sifat), and the correct motivation (inner tawhid al-ibada).
Having the correct motivation and annihilating hypocrisy is in fact a lifelong struggle for most people, and so there are very few who have completely perfected their monotheism (tawhid). However, every adult should have the correct knowledge and understanding, and that depends on choosing the right religion. Christians may avoid the outward shirk of worshiping other than God, and they may avoid the shirk of claiming that there is more than one Creator and Sustainer of the universe, but no matter how much you claim that the Trinity is One God, it still mixes a human being (Jesus) with God, and thus results in worshiping either a deified human being (Jesus as God) or a micro-god (God with Jesus's human characteristics) and this is not monotheism. You are worshiping a false image not the real God.
In summary, tawhid (i.e., monotheism) is a complete way of being. It must characterize every level on which human beings relate to God. If a person falls short on any of these levels, it is not truly tawhid. It goes far beyond avoiding the obvious errors of polytheism and idolatry.