Radisson finds the topic of religion painful because his Christian mother died when he was 12, though he had prayed and begged God to spare her life. This may be what led him to study philosophy so in depth that he ultimately became a philosophy professor, but his desire to now avoid the topic of religion does not mesh well with his career as a philosophy professor. His anger at God has him requesting his students quote Friedrich Nietzsche and, in exchange, he promises to allow them to skip the chapter on religion. This is not the only clue the movie makers give that they have read atheist material extensively. Radisson tells Josh that if he won't reach a consensus with the class, he must prove God is not dead. Radisson had already explained this was a metaphor and, taken in the context of Nietzsche's point, Josh does an excellent job of proving this.