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.
Men my brothers who live after us,
have your hearts not hardened against us.
For, if on poor us you take pity,
God will sooner show you mercy.
—Francois Villon, "The Ballad of the Hanged Men"
This is a version of the translation from the French of the epigraph that Capote chose for In Cold Blood. An epigraph is an appetizer for the book; it teases you into thinking about what's going to come in the book without filling you up.
So, what could a section from a poem entitled "The Ballad of the Hanged Men" have to do with a novel entitled In Cold Blood, which ends with the hanging of two men? Hmm.
We think that what Capote is doing here is setting us up for the central moral question in his book. What do we make of people who commit such shocking crimes? Do their lives have any moral standing at all? Is the death penalty morally justified? Do the condemned deserve pity, or at least, mercy? If you read the ending of this poem, you'll see that the men about to hang pray to Jesus for salvation for themselves. Perry and Dick had no use for religion. The men in the poem surely did. They believe that God demands mercy. Do you think that God is the only reason to show mercy?