Part 1: God LearnersYeah, the thing about the God Learners is that the basic power in Glorantha is myth. Myth is what drives literally everything. The God Learners were an empire in the Second Age of the world who worshipped the Invisible God Malkion, who for our purposes can be taken to be Jesus. They were monotheists who discovered the power of myth when they interacted with the other people.
And then they came up with the theory of the Campbellian monomyth, realizing that a lot of myths were really very similar, and that they could use this. They saw nothing wrong with messing up HeroQuests and in general being complete assholes on the mythic level for power, because those gods were all false. This allowed them to develop, incidentally, the RuneQuest Sight - a power that let them track connections between religion and magic and how they connected on the Hero Plane, where Hero Quests happen.
The biggest example here is the Goddess Switch. They found a pair of goddesses, Inika and Einhorn. The people of Wenelia worshiped Inika as a grain goddess, while the people of Slontos worshiped Einhorn. Via repeated HeroQuesting with extremely calculated mistakes, the God Learners brought their myths closer and closer together. They had to kill a few minor gods who wouldn't get with the program, of course. And eventually, they forced Inika and Einhorn to have to admit that they were long-lost sisters. Which they now were.
And then the God Learners performed a HeroQuest in which they "discovered" a new myth, in which the two goddesses swapped their husbands to prevent a great famine. They did this to prove that these false gods were essentially interchangeable, and thus that Malkion the Invisible God was the only true god. However, it also resulted in all of the grain in both countries dying, as each goddess oversaw grain that was not appropriate to the area...and all the marriages in Slontos lasted no more than a year, as they were sworn on the grain goddess.
They had also created the false deity Zistor, the Machine God. I won't talk more about that until we meet the Mostali, though. Suffice to say that the God Learners created a deity robot.
They also have their own much more powerful magic than most other groups: Sorcery. God Learner Sorcery is very powerful. Some rune magic is easier to learn, some divine magic is stronger, and dragon magic has a ton of advantages over it...but God Learner sorcery was the most versatile and flexible of all magic ever to exist. It is a large part of how the God Learners conquered so much of the world.
Among other things: it can rip open gates to the Hero Plane. No worshipers needed, no rituals, they just find the gate and tear it open by main force.