What is the theme in The Crossing by Cormac McCarthy?

The importance of doing what one feels to be right is the main theme. This theme is exhibited by Billy throughout the story, including his decision to return the wolf to her home. Billy seems to feel this is the right thing to do, though he doesn't express his reasons for believing this. Billy does what he believes to be right again when the wolf is taken from him. He waits for a chance to get the wolf back and goes so far as to trade his rifle for the dead animal in order to return her to her home. When Billy returns home and finds his parents have been murdered, he seems immediately set on the idea of going to Mexico to search for the men who killed them.