If it's God's will, then I will!

I saw this on a license plate (we're only required to have one on the back in Oklahoma, so people put vanity plates on the front) and what they mean is "if doing something is god's will then I will do it". My question is how do you know god's will?

I would say GOOGLE IT! Although Most people will say, "Pray about it and he'll tell you." Ok well that's reasonable. How does he tell you? Does he make you feel a certain way? Maybe he'll tell you audibly? Maybe he'll have you read a particular passage in the bible that day? (thus negating your free will)

When I was a kid there was a girl in Sunday school whose grandma got raped. She was in her 80's. The guy that did it got caught and he said he did it because he heard god tell him to do it. We can't prove he did, we can't prove he didn't either! I know that's bad logic, sorry. The point is who are we to punish him for something that's between him and god? Who are we to say god didn't tell him to rape that old helpless woman? Most people would respond to that question and say, "Well god only commands people to do honorable, nice, loving, etc. things" and I say turn your bible to Numbers chapter 31 verses 17-18!! It reads as follows

"17 Slay, therefore, every male child and every woman who has had intercourse with a man [so that means spare all the lesbians! ] 18 But you may spare and keep for yourselves all girls who have had no intercourse with a man" (NAS)

So god's army, led by Moses is destroying another tribe and taking all their girls who are lesbians or virgins! I wonder why they would only want THAT PARTICULAR type of girl? So some father will be killed and his virgin daughter will be defiled by an invading army led by Moses and his Hebrew god. Nice. Yeah god would never command someone to rape your grandma....