He is perfection. He is righteous. I don't know if He chose to be good or if he always has been, but being who he is has it's restrictions. He cannot lie. So, when he said he cannot be around evil, that means he can't. Not that he choses not to, but that he can't. He won't ever go back on his word, so when he said that, it became indefinite. Does this make any sense? If it isn't clear enough I will try to explain better. trust me though, the last thing I would ever say is that God is not omnipotent.