The Good Book is Uncle Dave's fictional Bible. In Postal 2, during the siege of the Compound, Uncle Dave comes out of the building to confront the ATF. According to him, the Good Book "told" him to make the ATF agents die, and then himself. This, however, was never fulfilled, since Uncle Dave never kills himself and relocates to Catharsis in Postal 3.
In the Postal film, the Good Book says that Apocalypse will begin with the rape of a "tiny entertainer" by a thousand monkeys, so Verne Troyer is thrown to a group of chimpanzees. After that, Richard, Uncle Dave's right-hand man, proceeds to shoot and kill Dave to initiate the extinction of mankind per the Good Book.