Seriously. How hard is this to comprehend? "Communing" with your magic sky daddy is "wisdom" and believing irrefutably that you are His will incarnate is totally "charisma", but memorizing lore of multiple religions and the fiddly details of all manner of adjacent facts is completely "intelligence"-based. I mean, fucking duh.

Shit, tons of religious people don't know much about their own religion.

Yeah exactly. And considering clerics are devotees of specific deities it’s not like they’re going to be experts outside of it. As a DM I assume clerics have a firm understanding of their god. You don’t have to roll to know anything I expect an ordained minister to understand about them. But just like I don’t expect a priest of Iuppiter to understand Cybellian rites or Saturnian prayers you’re shit out of luck about questions not relating to your god.

And in that vein basic questions about local religion should have a low dc, but cultural distance can increase it. That priest of Iuppiter may have reason to know about other deities in their region even secret ones, but knowing jack shit about Shiva is academic to them. Knowing anything about Zoroastrianism is on par with knowing history to them. They likely know a bit about Ra and Osiris, but only because those are basic facts about a significant nearby culture’s religion.

All the advantages that being a cleric provides here should be represented in the form of proficiency. But you aren’t studying this shit, you’re deepening your connection to your deity.

That said I do think there’s room for an int based holy caster in something like pf2. A religious scholar rather than cleric

Yeah, like the proficiency represents training and study, but an Int (religion) check usually involves knowledge of deities, mythology or symbology. That said, you might rule that a practical application of that knowledge, such as how to perform ceremonial rites, might constitute a Wisdom or Charisma check instead.

The issue isn't really there, but that it's also the check for knowing about your own religion.

DMs: if a character wants to know something about their own religion, a good solution to this is to just tell them, rather than requiring a check (or if you want the group to make checks for something obscure, give a bonus or a lowered DC to someone if they're a member of that faith.)

It was quite a cultural shock for me when I first met Americans vehemently claiming that Catholics aren't Christians.

In a fantasy setting I would actually expect a religious person to know a thing or two about their religion. Only in a fantasy setting though.

Right, but... while the requirement for INT supports "cleric who doesn't know anything about their religion" it also makes it significantly harder to play "cleric who does know something about their religion" - which probably should be more viable than "the wizard happens to know all this stuff randomly"

I was raised Mormon, and had always been taught that if you get to the highest heaven, you'll become a god and make your own world. Only after I left did I find out that that's not actual doctrine and comes from taking something that's supposed to be a metaphor literally. And any details about the church that look bad aren't going to be repeated by mormons, so mormons tend not to know about them.

Charisma is for making your own religion.

Remembering things is the primary purpose of the check, but sometimes how you're applying it might require an alternative skill check to make sense. Here are some examples (from https://rpgbot.net/dnd5/characters/impractical-skill-checks/ ):

Wisdom – Consoling and counselling a creature through a crisis of faith could be done with a Wisdom (Religion) check.

Charisma – Proselytizing for a faith makes more sense as a Charisma (Religion) check than a Charisma (Persuasion) check.

INT is a pretty powerful stat if your DM has done a lot of work to put lore into the world and then has plots that rely on it - and it's pretty good for monster knowledge checks. At the right table INT is probably the most important stat to have!

Having said that WIS covering perception means it needs no help.

The solution to sad clerics is to just assume they know things it'd be sensible for them to know, without a check needed, and reserve Religion checks for stuff that they wouldn't know, like "the stats of a mummy" or "the rites of Azmodeus"

Intelligence is just knowing things and being able to process things, so in theory knowing about religion would be intelligence, however in religion knowing the *significance* of things is much more important, so it should really be wisdom...

Low intelligence may mean you follow blindly, but ask the average religious person the reasoning for The Great Schism and they'll probably pull a blank. Ask an irreligious trivia expert and they'll probably be able to tell you about how it was a disagreement over some traditions and the powers of the pope and who it should be which resulted in Christianity splitting in two in the 11th century, but it would take wisdom to know why it was significant, and why Catholics/Orthodox have historically disliked each other less than either/Muslims, along with a bunch of other useful contextual information which is lost when regurgitating facts

That’s not even true. Highly intelligent people may feel it’s all bullshit, but a lot of highly important scientists were clergy. Hell often tracking the stars, reading, writing, pharmacology, medicine, and math were the responsibilities of the priestly class in ancient religions. Modern genetics was discovered by a monk. The pope currently has astronomers.

It's maybe a problem that everyone assumes fantasy religion should be based on modern Christianity...

In 5e, a religion check isn't to see how well you commune with your God. It's how well you know any given god's traits, domain, followers, plane, etc.