Philosophy Now Forum

Simple idea really.

If God is omniscient then he will know what will happen in the future. But if humans have free will this means that he knew which choices you would make in life... and that he always knew this. Meaning that the concept of choosing to be godly or sinful or whatever is a fraud. If you do have control over your actions, then God doesn't know what you're going to choose and so he isn't omniscient.

http://en.wikipedia.org/wiki/Free_will_in_theology

Lots of interesting takes on it there. I particularly enjoy the Jewish one where we are asked to except both premises as not mutually exclusive - because god is unknowable.