Now I've never really thought about this much, beyond the basic observation that clerics are boring, which you already knew.
Our game reflects this. Our clerics are pretty Christian, just like our characters are pretty modern and pretty western in their worldviews. Our clerics tend to have an evangelical habit. If there are followers of other religions in their same party, they try to convert each other, or they try to pick apart their respective imaginary religions with clever metaphysical arguments that no fantasy faith could possibly stand up to. They go on holy crusades against evil (the "fanatical fire and brimstone inquisitor type" being a classic result), and so on. It's really hard to see beyond your culture, you know? And in D&D this may or may not be a problem, depending on your goals.
For me it's mostly not a problem, in spite of what the preceding paragraphs may have suggested, as long as I don't have to play a cleric. Because clerics are boring. Which you already knew.
And actually, this post isn't about clerics.
It's about theists and theistic magic and cults and myths and rituals in RuneQuest. I'm trying to get a better handle on these things. And the first part of doing so is recognizing that theists aren't clerics. (Except when they are, of course, but that's on me for putting a Christian church in my RuneQuest game, and I get that.) The second part of doing so will be communicating the fact that theists aren't clerics to my group (with the ultimate goal of convincing them that theists aren't boring). But let's focus on the first part first.
So here's a thing. When the vikings were messing about in Northern England and Scotland and Ireland and places (I will stop this list here it will get too long), what were they up to? Well they were killing people and taking their stuff, and they were shaking down local big men, and they were burning things, and they were making great heathen armies, and they were calling places names like Something-by, and they were saying "their" a lot. So they were doing these things and other things, but it looks like they weren't evangelizing. You just didn't go around trying to convert people to worship of Odin. I mean, you didn't even extoll the virtue of Odin to Anglo-Saxons, who were getting pretty Christian by this time and should have known better! It just wasn't a thing you did as a matter of habit. Can you imagine that? Meanwhile, the Christians were busy extolling their doctrines to you. And eventually a bunch of people evangelizing about Christ managed to repeat their case enough and throw in enough fringe benefits (convenient church locations on top of your sacred sites, for starters, and some good Christian sacred kingship as well. Maybe wine? I don't know.) to get you to trade off your weird old gods for their one true God. What does that tell us? It tells us (among other things) that these heathen religions were different in this way from the frame we're used to using to think about religion.
And that's not the only thing that's going to be different.
So we don't actually have a lot to work with, in practical terms, other than a whole lot of conjecture and some imagery and a few words written about some gods hundreds of years later by Christians, and some actual objects that didn't happen to rot away and that we have found.
Ask me about the religious beliefs in Michigan a couple hundred years ago. We have really good records about this but if you tried to reconstruct the religious practices of 19th century Michigan people from what I told you about them after you first lost most of the pages of my notes, plus maybe a cross pendant you found, you'd be doing something sort of like what we're doing when we try to figure out heathen beliefs. You'd have conjecture and imagery and pieces of actual objects that didn't happen to rot away and that we have found.
Fortunately for us, conjecture and imagery pieces of actual objects that didn't happen to rot away are pretty good working material for fantasy gaming. Way better than they are for humanistic research because we don't actually have to try to say true things based on these scraps, we just have to do interesting things with them, where "interesting" is defined as "it worked at Friday night's game with my friends and was not boring, like clerics."
So that is a reasonable goal, and I will adopt it.
But this post is long enough, so I'll drop some images in and post it. I will come back with something more constructive later, using RuneQuest to structure it. I can't promise I'll follow up soon (the beauty of blogging is that it's on my own schedule, and my schedule is slow). But I promise I will get back to trying my hand at this. I have started. In the meantime, my first draft attempt at a pseudo-viking-y cult is this Cult of the Gullet. It's still underspecified for a RuneQuest cult, but it's a gesture in that direction.
In the meantime, feel free to tell me that this has already been done, and where this has already been done, and who has already done this. Glorantha, I know, this is Glorantha's whole thing, so of course it's no accident that RuneQuest is making me think about it. Others?