the qur'an as a document of prophethood

The Qur'an refers on several occasions to the fact that it is the word of God, that it issues from a divine source in the very words in which the Prophet received them and which he later transmitted. The divine nature of the qur'an is affirmed in several verses.
in lii:33-34 we read, "or they say that (the Prophet) is inventing it. Indeed they do not believe. If they are truthful then let them produce words like it". likewise in xvii:88 "Say (O Muhammad), if all the jinn and mankind were to join forces to produce something like this qur'an they could not produce it even if they were to help one another." again, in xi:13 "or they say he has invented it! Say: then produce ten verses like it which you have invented," and again in X:38, "or they say he has invented it. Say: produce a single chapter like it," we find further proof.
the following challenge is made in chapter ii:23 "and if you are in doubt concerning that which we have revealed to Our slave then produce a chapter like it. "
Here it should be noted that the Qur'an is addressing those who grew up with Muhammad, the man they knew to be unlettered and untutored in the matters spoken about in the Qur'an. Despite this knowledge, they still doubt.
Another challenge is issued, (to those who would find contradictions in the qur'an, but obviously cannot): Will they not reflect upon the Qur'an? If it had been from other than God, they would have found in it much incongruity [iv:82].
Since everything in the world is in a state of growth and self-perfection, then the Qur'an would of necessity lack harmony since it was revealed over a period of twenty-three years; it would lack harmony that is if we were to suppose that it was the work of a man rather than of a prophet. The Qur'an, whose messages announce and confirm that it is the work of God, also teaches us that Muhammad is a messenger, sent by God, thus confirming the authenticity of the Prophet. In chapter XIII:43 God speaks Himself, as on many occasions, confirming that He is witness and testimony to the prophecy of Muhammad: "Say God is sufficient witness between you and me." the verse refers to disbelievers and defies their disbelief.
In another verse, the testimony of angels is added to that of God's: But God testifies concerning that which he has revealed to you; He has revealed it in His knowledge; and the Angels also testify. And God is sufficient witness [iv:166].