Exodus from the Long Sun by Gene Wolfe

Wolfe's recent multi-volume novels have invited interpretation as religious allegory. In the "Book of the Long Sun," the fourth volume of which is Exodus from the Long Sun, religion is at least an inspirational starting point. This book is set on a starship, the Whorl, whose inhabitants have lost track of the fact that they are on a journey. Indeed their origins are mysterious to them, and the starship's vestigial communications system is understood to bring messages from unknown gods. One priest, Patera Silk, discovers the truth about the Whorl, and the gods his people worship. Silk must prepare his people for the revelation.