p1) As an omniscient being, God knows everything.
p2) If God knows everything, then He must know what I’m going to do before I do it – for example, drink beer
p3) If God already knows that I’m going to drink the beer before I do it, then it must be true that I drink the beer
If it’s true that I drink the beer, then it can’t be false that I drink the beer.
c1) In other words, I don’t have a choice. And if I don’t have a choice to either drink or not drink the beer, then I don’t have free will.