"He liked a book. Pilgrim's Progress."
Pilgrim's Progress
Public DomainPilgrim's Progress

Pilgrim's Progress is a 1678 novel by John Bunyan.  Written during a stint in jail for holding religious services outside of an established church, it is laden with religious metaphors and has remained immensely popular ever since its publication. 

There are parallels to the Joads' story, as the main character Christian journeys from the 'City of Destruction' to the 'Celestial City'.