There are more than 22 million sentients between the Shan Shan mountains and a line formed roughly by Winterwood, the Nidan Mountains and Lake Felster. These are the heirs of those briefly united by the High Council of the Lands of Genertela (and more or less by its successor the Third Council). That’s the system of theism presented in the Cults books – polytheistic, with initiation to a single deity’s secrets being the foundation for spiritual insight. At this level, Lightbringer, Earth, Lunar, Solar, Darkness, etc., are all pretty comparable.
These cults are aware of each other to a greater or lesser degree. They might have public and private names for each other, but most of the cults presented in the cults books are aware of each others existence. If you read the mythos and history of each, you find that they overlap and collectively form a pattern.
These peoples are mostly human, but almost a fifth are not. Aldryami, mostali, trolls, and others cooperated with the Theyalan and later councils and shared many of their stories. Aldrya, Kyger Litor, Mostal, and Zorak Zoran are all known and other cults have both human and nonhuman members.
There are other spiritual approaches however. Along the western coast of Genertela there are somewhere around 7 million peoples who have a decidedly materialist and rationalist approach to spiritual understanding. They reject that devotion to a “lesser” deity should be the foundation of spiritual insight; instead their great prophet Malkion revealed that the cosmos can be rationally understood and tasked magical specialists with that responsibility. An abstract and distant Invisible God created and unifies the cosmos – this is the One above all the lesser deities.
Now the Malkioni are perfectly aware of many of the cults of central Genertela – particularly the Lightbringers, Earth, etc. However, they rely upon their magical specialists to handle the more powerful (and spiritual dangerous) magic, and call upon spirits, heroes, and petty deities to aid them in daily life.
East of the Shan Shan is another 16.6 million sentients. They are quite similar to the central Genertelans, with many of the same cults (particularly among Earth and Solar). However, like the Westerners they have their own magical specialists but these deal with magic taught to them by the dragons – or even are True Dragons. This gives many of them a radically different outlook from the rest of Genertela – although most people are initiated into the secrets of their cult, true spiritual insight comes from those who can harness the powers of the cosmic dragons.
There’s a lot in there to unpack, but hopefully this complements the Mythology book nicely.
What I encourage folk to do is not to think of the various religions in Glorantha as being hermetically sealed, but instead in constant communication with each other.
We can think of different human cultures being d made out of cult-monads, which are universally acknowledged throughout the setting even if many are worshipped only in localities. The cluster of cults in a greater community form the culture and even the languages used. But we can travel from Felster Lake to the plains of Pent and find overlapping symbols and iconography.
That last paragraph is a guide to understanding Kralorela and Ignorance (Teshnos as well – although it has little to no Dragon influence):
East of the Shan Shan is another 16.6 million sentients. They are quite similar to the central Genertelans, with many of the same cults (particularly among Earth and Solar). However, like the Westerners they have their own magical specialists but these deal with magic taught to them by the dragons – or even are True Dragons. This gives many of them a radically different outlook from the rest of Genertela – although most people are initiated into the secrets of their cult, true spiritual insight comes from those who can harness the powers of the cosmic dragons.