It's the difference between being a baseball player and being the guy who develops a better system for the quantitative analysis of baseball players.

With that said, characters should automatically know the basic rules of their own religion without having to roll, unless they're remarkably ignorant. Rolls are for knowing about obscure cults, deciphering ancient inscriptions, or negotiating with extraplanar beings, not for trying to remember whether or not you're supposed to love your neighbor.