The Quran is the direct words of Allah, here's a couple verses from chapter 2:
"2. This is the Book; in it is guidance sure, without doubt, to those who fear Allah.
3. Who believe in the Unseen, are steadfast in prayer, and spend out of what We have provided for them;
4. And who believe in the Revelation sent to thee, and sent before thy time, and (in their hearts) have the assurance of the Hereafter.
5. They are on (true) guidance, from their Lord, and it is these who will prosper.
6. As to those who reject Faith, it is the same to them whether thou warn them or do not warn them; they will not believe.
7. Allah hath set a seal on their hearts and on their hearing, and on their eyes is a veil; great is the penalty they (incur). "