God introduced him self to men and what is your concrete evidence that god did such a thing ?
Through established traditions in human history, through books given to communities culminating with the Quran. At least, one would be wise to examine the claims without dismissing them first hand.
It seems human beings no matter when and where they lived, they worshiped God the right way or the wrong way, but God was There amidst them. Greeks had many Gods, Romans similar. Mention any civilization, they worshipped something/someone they named god.
It is human to worship. It is as if we are born with the instinct to worship God. Islam at least teaches so.