Almighty Allah (swt) sent the knowledge of revelation, which sheds light on human life, through the prophets He chose. This process started with the first human, Prophet Adam, and continued with Nuh (Noah), Ibrahim (Abraham), Musa (Moses), Isa (Jesus) and many other prophets whose names we cannot count. The fact that Allah (swt) sent revelations to the prophets is stated in the verse as follows: “Indeed, We have revealed to you, [O Muhammad], as We revealed to Noah and the prophets after him. And we revealed to Abraham, Ishmael, Isaac, Jacob, the Descendants, Jesus, Job, Jonah, Aaron, and Solomon, and to David We gave the book [of Psalms]. (Nisa 4/163)

Revelation means “Allah's (swt) quick and secret notification of an order or information to His prophet”. In this sense, the phenomenon of revelation is a special situation between Allah (swt) and the prophet. Therefore, only prophets really know the psychology of receiving a revelation. As a matter of fact, when the Prophet Muhammad (saw) was once asked how the revelation came to him, he replied: "Sometimes it is (revealed) like the ringing of a bell, this form of Inspiration is the hardest of all. And then this state passes off after I have grasped what is inspired. Sometimes the Angel comes in the form of a man and talks to me and I grasp whatever he says." (Bukhari, Bad'e al-Wahy, 1)    

The angel who delivered the Qur'an to the Messenger of Allah (saw) is Jibril (Gabriel). No one else can intervene in the relationship between Allah (swt), Gabriel (as) and the Prophet Muhammad (saw) in the process of conveying the revelation to man. It is not possible for the Prophet Muhammad (saw) to make any changes in the revelation that came to Him. In that case, the revelation remained under full protection until it was conveyed with tabligh from Allah (swt) to the Prophet Muhammad (saw) and from him to man.

All divine books delivered the same essence and the same message to humanity. There is no difference between their belief in Allah, belief in the Hereafter and moral principles. Because they all come from the same source. Their names are also common and it is Islam. 

Why were Different Books Revealed? This question can be explained in two ways: 

First, over time, people have differed in understanding the divine books that have been revealed to them, and they have attributed meanings that are incompatible with the divine books. In fact, over time, they changed some divine commands and carried out tahrif over them, and they deviated into beliefs and practices that were incompatible with the essence of the book. (Baqarah, 2/213) Therefore, Almighty Allah (swt) sent a new prophet. 

The second reason is this: There are differences in customs, traditions and social life in the societies to which the prophets were sent. Therefore, although the main subjects of divine religions are the same, there have been differences in some orders, prohibitions, halal and harams.