first of all, we are talking about some concept of god that is uncomprehensible by nature. If you want to rationally prove there is or is not a god, you have to have some evidence of it, and since there isn't any, there is no reason to believe god exists or doesn't exist for any reason based in rationality. that's why people don't think there's a god, they BELIEVE in god. According to the Christian bible, when you believe in god, you know god. I don't think it is much different in any of the western texts.