Epigraphs are like little appetizers to the great entrée of a story. They illuminate important aspects of the story, and they get us headed in the right direction.
"Th' inclosure narrow'd; the sagacious power
Of hounds and death drew nearer every hour."
- John Dryden, From "The Hind and the Panther, The Second Part"
What's up with the epigraph?
Sounds like a description of the priest's struggle, doesn't it? His path becomes narrower as the novel progresses, until he decides that he has no choice but to walk towards certain death. This alone makes it a worthy epigraph, but there's more: Dryden's poem, "The Hind and the Panther," is largely about Catholicism and its conflicts and controversies in the world. Like Greene's The Power and the Glory, it presents the Catholic Church as an ultimately indestructible institution that will rise above religious divisions and conflicts. Like Celine Dion, its heart will go on, even if it sinks from time to time after colliding with an iceberg. In Dryden's time, the Church faced political and religious pressure from Protestantism. In Greene's time, atheism.