What is Skippey asking Fred to debate on at the next Disobligers' Society's meeting? Why does he ask Fred to take this side at the debate? What are the religious beliefs of Fred's debate opponent?

Skippey asks Fred to debate in favor of the "soul" at the next Disobligers' Society's meeting. Skippey is asking Fred to debate on the side of the "soul" because he knows that Fred does not have any use for the soul's existence. Fred's opponent is a believer.