Telling God What He Can Do

For a religion that claims to view their god as the most powerful, supreme being in the universe, some Christians have an interesting habit of placing restrictions on what he can and can't do.

God can't make a world without suffering, he has to inspire a collection of written texts (that have no mistakes in them), and he certainly can't be sympathetic to anyone who practices other religion. But where do these limitations come from, and what purpose do they serve? In short: who says?