Christians believe that God doesn't change reality just by willing it. No one really knows how he supposedly created the universe. The theory is that Jesus doesn't perform miracles by bending the laws of nature. I'll explain: Potassium + water = big explosion. But if you added something to the water or to the potassium, you could keep it from exploding. So, on earth, nothing ever happens to water that will turn it into wine. But if God exerted a supernatual force on it, it would, without bending the laws of nature. The idea is that the laws of nature incorporate supernatual meddling, but these are laws that we may never discover because we can't meddle with things supernatualy. God doesn't change reality. And anyways, the Guardians thought that God was all-powerful, and that humans weren't, so I'm not even sure they're thoughts went down that road.