1. God is omniscient and knows therefore beforehand as an eternal truth each choice (action) that each human will decide on. If this is the case then humans cannot freely choose (act), otherwise than in the way God knows they will ( and if they do act contrary to Godís knowledge, then God can not be omniscient). If God knows humansí sins before they commit them, and the sins must occur according to Godís knowledge, then how can humans avoid those sins, and how can humans be said to have free will?
2. If God has complete foreknowledge of everything that will happen, and is also omnipotent, then God must have organized all things to happen the way in which God has foreknowledge that they will happen. If this is the case then how can it be maintained that humans have free will.
(From: Harper Collins Dictionary Philosophy, Peter A. Angeles)