During a discussion about clerics and religion in D&D, someone complained about St. Cuthbert. He's a saint, obviously, but where are the other saints, and what church is he a saint of?
I don't know if the person asking was aware that St. Cuthbert, regardless of any Gygaxian embellishments, was a real historical figure. Let's assume he *was* aware, and that he's only asking about the in-game Cuthbert. Let's also assume that he's aware of the possible answer "default clerics were more or less Christian monks in Gary and Dave's games" and that answer isn't good enough, because Cuthbert survived in later books and was turned into a god, but other Christian trappings were eliminated.
I'll argue that the lack of context for St. Cuthbert is a feature, not a bug.
St. Cuthbert, because he's called a saint and thus evokes an image of a medieval Catholic setting, creates sketchy details about the setting without making anything explicit. There's a void around St. Cuthbert, but it's a pregnant void; players have a vague idea what else is going on in the world. If they want to explore that, they can, and the details get filled in as they play.
The other way to approach this, the way I suspect some people are expecting when they complain about that pregnant void, is to detail all the information about the church in the campaign: when was it founded, how far has it spread, what's the hierarchy like, where are the internal conflicts.
The problem with that approach is: making up all that stuff can be fun. Yeah, that's a problem. Because one person making up all the details might have fun, but when that's finished, the fun is all "used" up. There's not much left to do when the material hits the table.
So leave the pregnant void alone. It will bear children in plenty of time.