Prophethood is a sublime status granted only to those who are chosen. A prophet deals with the heart and souls of humans; it is, therefore, a delicate matter to believe in the one who claims prophethood. Hence, there should be a sign that lets people recognize a real prophet from a fake one; that's "miracle." A "miracle" is an extraordinary act or event that no other human, from the first to the last, can perform it or cause it to happen, except a prophet. It can be neither explained by natural or scientific laws. For Prophet Muhammad (PBUH&HP), the Quran is known as an everlasting miracle that is the most outstanding of Prophet's (PBUH&HP) miracles. The question is: why the Quran is considered as a miracle? Let's find out the reasons.

1. The Quran Is Unique in Style and Inimitable

The Quran is revealed with great eloquence and fluency to convey the message. Precise, poetic, targeted, and meaningful terms used in the Quran are such that no weakness of expression can be found in any of its Ayats. In fact, the words are chosen such that they express the desired meaning in the best way possible (Fasaha) with the minimum usage of words (Balaqa). And, these are features that scholars of Arab literature have noticed in every chapter of the Quran [1]. 

What makes the Quran a miracle in this regard is that, until the present, no one has been able (and no one will be able) to bring even one short Surah similar to that of this holy book. A Surah that could express the highest scientific facts in simple, comprehensible words and describes different aspects of a scientific matter as clearly as possible. This is an issue that has already been addressed in the Quran: "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). There is no historical account of those who succeeded in defeating this claim of the Quran. If there existed any, those who have always challenged the origin of the Quran should have recorded it. 

2. The Quran has been Brought by a Prophet Who Was Uninstructed (Ummi)

According to both historical records and the Quran, Prophet Muhammad (PBUH&HP) was Ummi before he was chosen as a messenger of Allah Almighty; he hadn't been taught by any teacher to read and write 1]. "You were not able to read or write before the Quran was revealed to you; however, the followers of falsehood would have tried to confuse the matter" (29:48). Therefore, the Quran that its words are in extreme eloquence and fluency and reveal sophisticated concepts cannot be Prophet's (PBUH&HP) word. Hence, it is a divine work gained through revelation, a "miracle." 

3. Scientific Facts Revealed by the Quran 

The Quran is not a book of science or a specialized book, nor has it aimed to concentrate on scientific facts. However, these kinds of information are stated in the Quran to demonstrate the wonders of creation and Allah Almighty's glory. 
In this regard, the creation of humans is described in detail in the Quran (23:12-14). In the first step, the human being was fashioned from clay. Other measures include the creation of man from spurting water, a drop of semen, the sperm fashioned into an embryo, this embryo fashioned into a shapeless lump of flesh. From the lump of flesh, fashioned bones, clothed the bones with flesh and then created the consanguinity and affinity [2].

The movement of the earth is another fact mentioned in the Quran: "It is Allah who raised the heavens without any pillars that you see" (13:2). In this verse, it is mentioned that there exist invisible supports that raise up the heavens. These supports are now referred to as the gravitational and other unseen forces in the universe. This scientific fact that is valid today was unknown in that era, and even one thousand years later when Galileo explained this fact and was sentenced to death. That's why it is not explicitly stated in the Quran; otherwise, it would have been banned [1].

4. Accurate Predictions 

Some accurate predictions are among the verses of the Quran. This proves that it has been descended from an absolutely knowing source that can report the unseen.

As an example, in the time of Prophet Muhammad (PBUH&HP), Mecca was controlled by polytheists for a while. They did not let Muslims enter the city and do the Hajj rituals. Then, Prophet (PBUH&HP) dreamed that he succeeded in performing Hajj with his companions. This was confirmed in an Ayah: "Certainly Allah has fulfilled His Apostle's vision in all truth: You will surely enter the Sacred Mosque, God willing, in safety, with your heads shaven or hair cropped, without any fear." (48:27). In the next year, this dream came true. 

In another case, the Quran has predicted that: "Byzantium has been vanquished in a nearby territory, but following their defeat, they will be victors in a few years." (30: 2-4). Some years later, both predictions came true. 

From what has been discussed above, it can be deduced that the Quran cannot be written by a human being. It is undoubtedly from a superior all-knowing all-wise source, which is Allah Almighty. Consequently, the Quran can be considered as one of Prophet Muhammad's (PBUH&HP) miracles, the greatest one, of course.

 References:

1. Quran
2. H. El-Ramady, et al., "Soils and Human Creation in the Holy Quran from the Point of View of Soil Science," Env. Biodiv. Soil Security, vol. 3, pp. 1- 9, (2019).
    

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.