The authenticity of the Quran

The Quran, the last revelation of God to mankind, has remained free of change or human intervention for more than fourteen hundred years.

This Final Message of God was revealed to the prophet Muhammad, peace be upon him, for twenty-three years in a segmented way, so that in each revelation he was given one or several verses of greater or lesser size.

Each time the prophet Muhammad peace be upon him he received one of these revelations he recited to his disciples or companions, who collected it in writing and memorized it. The prophet, moreover, was indicating to them the exact position that each segment should occupy in the final compilation of the Text. In this way, hundreds of followers of the Prophet wrote or memorized the entire Qur'an even in the lifetime of Muhammad peace be upon him. After his death, Abu Bakr, the first caliph, put Zaid Ibn Zabit in charge of compiling everything it in a single volume as a unit work.

Later, and by order of the third caliph, Uthman ibn'Affan, seven copies were prepared and sent to the main urban centers of the Islamic world.

The survival of the Koran in its original Arabic form, living language and use; the existence of millions of people who have memorized it scrupulously and accurately in the four cardinal points and the perfect coincidence of one and the same text in all its copies and manuscripts are conclusive proofs of the authenticity of this, the last Revelation of God to humanity.

The Quran, all of it, in form and sense, letter and spirit, without any addition or loss is the Word of God. If Allah ordered the prophet Muhammad to say "Say: God is one!", The prophet could not but repeat the mandate, including even the imperative "say", which are kept in the book.

It is evident to anyone who reads the Qur'an that it is entirely dedicated to affirming the divine oneness. It is not, as some believe, a song to the feats and greatness of Muhammad peace be upon him. 
Whoever reads the Holy Qur'an should accept that in this Book there is no other desire or interest than to invite faith in the oneness of Allah, to praise, glorify and obey Him:

Allah exalted says it says in the Qur'an:

"Muhammad is not but a messenger. [Other] messengers have passed on before him. So if he was to die or be killed, would you turn back on your heels [to unbelief]? And he who turns back on his heels will never harm Allah at all; but Allah will reward the grateful."

Quran 3: 144