Who is Frank and the Tragedian from The Great Divorce and what is their importance?

Frank and the Tragedian are fragments of the same person: they are different spirits. When Frank's wife Sarah, who is bright and beautiful, comes by in a procession, these two fragments of a person try to make her feel pity for them. She no longer falls for their blackmail. Frank cannot physically fit into Heaven because he refuses to let go of his pain.