The "Great" or sometimes The "Good" Book of Mogadore was written by Setrákus Ra and contains all Mogadorian wisdom and ethics.
All Mogadorians must learn and live by this. However, it is likely that, as it is written by Setrákus Ra, it is a form of indoctrination of the people, who are capable of compassion and are not entirely violent and blood lusting. Such examples include Adamus Sutekh and, seemingly who had a relationship with Lorien and gave some aid in the development of humankind.
In The Revenge of Seven, Setrákus Ra attempts to force Ella to read the book to little avail. Ella rips the pages apart.
In United As One, following Setrákus Ra's death, a number of trueborn Mogadorians that had surrendered reject the teachings of the Book and burn it at the Mogadorian Prison Camp.