Now that we have gone through the axiom of monotheism and accepted it as a logical and rational principle, we should note that this belief is much more complicated than it seems. In order to reach a firm belief in the existence of God and His Oneness, one has to follow each of its stages.

These degrees include “unity of the essence of Allah”, “unity of the attributes of Allah”, “unity in what Allah does” and “unity in worship”. The first three of these belong to the realm of theoretical monotheism, while the last one is among practical monotheism. Here we will have a brief look at each of these steps.

1. Unity of the Essence of Allah

This stage of monotheism is defined as believing that God is One and Unique in His essence. The very first thing that one assumes regarding Allah is that of His Self-dependence; He is a being who is not dependent on any other beings in any way, while everything depends on Him and seeks His help.

Secondly, one has to believe in His Creatorship; that He is the creator and the ultimate source of all the existing things, all things are from Him, and He is not from anything. Accordingly, He is called the First Cause. The unity of essence, thus, means that this being is not multiplicable, and there is nothing like it. Since the self-existing truth is one, then this world has only one source and one end; it has neither originated from various sources nor will return to various ones, the whole universe has one center, one pole, and orbit.

2. Unity of the Essence and Attributes of Allah

It is defined as the recognition that the essence and the attributes of Allah are identical and that His various attributes are not separate from each other. While the Unity, in essence, refers to God’s Oneness, denying the existence of any peer or like for Him, the Unity in attributes means the negation of any kind of multiplicity or plurality within His essence.

All the attributes implying perfection and beauty belong to Him, and they are not at all separate from Him. The separation of the essence from the attributes and their separation from each other are the characteristics of a limited being, while God is infinite and such characteristics cannot be ascribed to Him. Accordingly, Allah has attributes which are unlimited – like His own self – and identical with His essence.

3. Unity in What Allah Does

The Unity of His work is to recognize that the world with all its systems is the work of Allah alone and has originated from His will only. Nothing in this world has occurred on its account and independent from God; every agent, cause or power owes its existence and effect to Him.

As He has no partner in His essence, He has no peer in what He does either. While human beings, as one of these agents and causes, have control over their own actions and can influence their destiny, they are not at all out of God’s will and supervision; otherwise, we should consider them as God’s partners, which will ultimately deny God’s unity in essence.   

4. Unity in Worship

Reaching this stage is when one only worships God and has prepared himself for praying Allah, the One. Based on Islamic doctrine, the act of worship has its own degrees, the clearest of which is the performance of the rites for Allah’s glorification and exaltation.

According to Holy Quran, worship is not limited to the actual performance of prayer but includes any form of spiritual orientation and idealization; the person whose purpose and motivation in life only satisfies his own whim has, in fact, led his spiritual direction toward it and thus worshiped it instead of God. So, the unity in worship is to see Allah as the only one who is fit to be worshiped and obeyed unconditionally and regard Him as the only purpose and direction of one’s conduct.

What Is the Difference between Theoretical and Practical Monotheism?

The first three degrees are all theoretical and a matter of creed - they should be recognized and acknowledged, and require rational thinking- while the fourth one is practical and a necessity for all of our actions.

Moreover, theoretical monotheism gives an insight to perfection while practical monotheism is the actual movement toward it; it is only seeing God’s Oneness and finding knowledge about it while practical monotheism is experiencing and feeling these beliefs tangibly in all walks of life.

In other words, theoretical monotheism provides the basis and foundation of practical monotheism; on the other hand, without bringing those beliefs into action, they would become deficient and imperfect.

Allah Almighty is the all-knowing all-wise creator. He has considered a unique way of perfection for every creature and then guided it to reach its excellence (20:50). Human beings, as autonomous creatures, are in real need of divine guidance to know how to live a perfect and purposeful life. According to Islamic beliefs, the Quran is the divine revelation to Prophet Muhammad PBUH&HP that contains necessary guidelines for human beings: "As We sent to you an Apostle from among yourselves, who recites to you Our signs, and purifies you, and teaches you the Book and wisdom, and teaches you what you did not know." (2:151). The question is that, is the Quran Allah's words? Let's see why the answer is: Yes. 

1. The Holy Quran and the Prophetic Narrations are Not of the Same Style

If the Quran was Prophet Muhammad's PBUH&HP words, his PBUH&HP narrations should have been of the same eloquence and beauty of the Quran. But that's not the case. The Quran is unique in style, expression system, and arrangement. And that's why no one has been able to bring even a chapter (Surah) similar to that of the Quran. As the Quran says: "And if you are in doubt concerning what We have sent down to Our servant, then bring a Surah like it, and invoke your helpers besides Allah, should you be truthful." (2:23). Although the prophetic narrations are articulate and eloquent, some of them have been imitated and distorted, unlike the Quran [1].

2. Prophet Muhammad PBUH&HP Never Claimed These Words to Be His

If the Quran were Prophet Muhammad's PBUH & HP words, it would have been logical for him to claim that these eloquent words were his. Consequently, he could have promoted his position, fascinated his opposers, and gathered more followers. But, he never intended to be considered and praised as a superior power. On the contrary, in one instance, someone came to him and was uneasy because of his magnificence and grandeur, he said: "Calm down! I am not a king" [2]. 

3. The Objection of Prophet Muhammad's PBUH&HP Oppposers Were not Answered Immediately  

In some of the Quranic verses, the objections and disagreements of Prophet's PBUH&HP opposers are answered. If the Quran was Prophet Muhammad's PBUH&HP words, all these verses should have been quickly revealed right after an objection was raised, or when he was insulted or oppressed. But, this was not always the case [1]. 

For example, the Qiblah at the time of Prophet Muhammad PBUH&HP was originally the Noble Sanctuary (Al-Aqsa Compound), similar to Judaism. That was a reason for Jews to mock Muslims and say that Muslims follow them; hence, they are superior. Prophet PBUH&HP waited 16 months for the divine revelation to let him change the Qiblah while he was disturbed by Jew's words. It was after such a long delay that he received a response: "turn your face towards the Holy Mosque, and wherever you may be, turn your faces towards it!" (2:144). If the Quran was Prophet Muhammad's PBUH&HP words, he could have changed the Qiblah much sooner and suffer less. 

4. Some Verses of the Quran Warn Prophet Muhammad PBUH&HP

In some of the verses of the Quran, Prophet Muhammad PBUH&HP is warned. In Surah Tawbah, he is told that: "May Allah excuse you! Why did you grant them to leave [to stay behind] before those who told the truth were evident to you, and you had ascertained the liars?" (9:43), or in another Ayat: "A prophet may not take captives until he has thoroughly decimated [the enemy] in the land." (8:67). Is it logical at all that someone blames himself and makes it public?

5. Prophet Muhammad PBUH & HP Was not Able to Read and Write

Prophet Muhammad PBUH&HP was not literate, and this is stated in the Quran and historical records. "You did not use to recite any scripture before it, nor did you write it with your right hand, for then the impugners would have been skeptical." (29:48). So, how can someone illiterate bring such eloquent words?

6. There is no Contradiction in the Quran

This holy book was revealed for 23 years. And something astonishing about the Quran is that there is no contradiction among the verses of it. If it was a human's words, there surely existed contradictions and errors in the Quran because human beings are forgetful, and for example, they forget what they told two years ago. But, this is not true about the Quran.

 References:

1. Allah's words
2. M. H. Hakimi, et al. "Al-Hayat," vol. 2, Translation: A. Aram, Iran, 1986.