From the publisher's blurb:
The divine cults are at the very core of life in Glorantha & thus this RPG. Much of the unique flavour of Greg Stafford's creation flows from these organizations.
The Cult rules in Tales of Prax are the basic ones for lay membership of some of the common cults. They allow you to quickly create a Hero & get playing. The rules in this supplement expand on this & create paths for the Heroes to follow as they develop.
In this supplement there are full descriptions of these paths for a few of the most common cults. Others are described in the same format in other supplements.