From the back cover:
ENTER THE TIME OF MYTH AND LEGEND.
Cults of RuneQuest: Mythology is an indispensable history of the mythology of the storied and epic Bronze Age fantasy world of Glorantha.
An explanation of myths and mythology and how it works in Glorantha.
Dozens of Gloranthan myths, ready to be reflected on your game table, and to give further context to the mythical history of the world.
A system-free book, Mythology is perfect for any RuneQuest player or gamemaster, any fan of Glorantha, players of other roleplaying games, and anyone with an interest in creative mythology.
This supplement is an enhancement to Cults of Glorantha [sic]. It is intended to provide a greater understanding of the rich and textured mythological world of Glorantha.