The Stories - 28:46
Nor were you on the slope of Tur when We called out (to Moses). But (We inform you) as a mercy from your Lord that you may warn a people to whom no warner came before you, that they may take heed.
In the context of verses 44,45,46; You were not aware of the previous books and therefore of this knowledge, otherwise the disbelievers would have an excuse that the Qur'an was fabricated:
The Spider/29:48
You did not read any of the previous books, nor did you write them with your hand. In that case, there would have been a pretext for those who advocate falsehood to be suspicious.
The Heights/7:157
Indeed, they follow (when the time comes) that messenger whom they find written in the Torah and the Gospel with them, the Messenger of Allah, the Messenger of the Ummim (who has not read the Torah and the Gospel), who enjoins upon them good and forbids them from evil, who makes lawful for them good things and forbids for them unclean things, who removes from them the weights and the fetters that weigh them down. Those who believe in him and respect him and help him and follow the light sent down with him are the successful ones.
Council/42:52
So We revealed to you a spirit from Our Presence, and you did not know what a book was and what faith was. But We have made it a light that guides the servants whom We will to the truth. Surely you are a guide to the right path.