Do We Need The Quran To Believe In God?
I think we need Quran to know Allah better and to know what he wants from us. We have example of people of Kahf, they did not get any Devine knowledge but they follow their fitrah. And Quran is Also Hujjat for us.
These are all natural steps. If you want to know who God is or what He wants from us, you would naturally want to investigate the claim of those who tell you that they have been appointed by God. Once established on the basis of evidence that the claim of prophets is true, then again the natural thing is to read the scripture that they gave us. Of course we need the scripture and the prophets in order to conclusively establish God, but the evidence of God is a-priori as well as empirical.