What does Banquo represent?

Banquo is the Corsican that Jozef meets in prison, a man who has been in prison so long that nobody can remember what he did to get there. He and Jozef begin to talk daily, and after Jozef tells him of his nightly visions of Zlee and his mother and all of the men he killed in the war, Banquo urges him to forgive himself and stop heaping guilt upon his head. Later, when Jozef thinks of Banquo he thinks, "he freed me."