What is the theme in The Dead and the Gone by Susan Beth Pfeffer?

One of the major themes in the novel is that of religious faith. The entire Morales family is religious and all the Morales children attend Catholic school. Based on their involvement with the church, it is a fair assumption their high level of faith has been passed to them from religious parents. This faith becomes not only a huge benefit to the family throughout the novel, but also a difficult thing to maintain in a difficult world.