What is the theme in Lamb: The Gospel According to Biff by Christopher Moore?

Spiritualism versus materialism isa the main theme of the book. Confusion exists on just what the Messiah is supposed to do for Israel. The Zealots think that Joshua will drive the Romans out of the country and restore the Jewish kingdom on earth. However, the politics of earth are of no concern to the Messiah. He has been sent to open the kingdom of Heaven to all humans, regardless of birth origins or politics. The implication is that God is tired of dealing with free-will humans, and thereby sends the Son to handle the situation of ancient people gone wild.