From the introduction:
The Lords of the Higher Worlds derive power from their human followers. This power feeds them, just as mortals eat food and drink wine. And, since the Balance binds the gods to not act directly in mortal affairs, the human followers are needed to spread their master's influence in the world of the living. This text deals with those who put the needs of the gods before their own.
The first section is for players. It lists most of the cults of Chaos active in the Young Kingdoms, and the nature of the average cult member. It also gives detailed instructions for making and playing a member of that cult. There are new spells, demon breeds, and goals for new characters.
The second section is for the Gamemaster only. It has further background on the cults, plot hooks and assorted tools for integrating the cults of Chaos into an ongoing campaign. Players should stay away from this section, as the knowledge contained therein is only for minds that have undergone certain preparations. Gamemasters will also find new enchantments, spells, and demons for their own use, either as player-character rewards or new and terrible foes.