From the Publisher's Website:
The Gamemasters' Edition of the Triune Corebook has all the stuff from the Quickstart, the Players' Edition, and more. The setting is explored in detail, including entries on each nation and the current political and criminal situations therein, special powers only available to angels and devils, NPCs, secret organizations, advice on running the game including using different playstyles, and an adventure for players. Obviously, it's designed only for Gamemasters but anyone can read it.