Symbolism, Imagery, Allegory
At one point, after White says he didn't go to his father's deathbed, he and Black have the following exchange:
BLACK: …I just get more amazed by the minute, that's all. How come you cant see yourself, honey? You plain as glass. I can see the wheels turning in there. The gears. And I can see the light too. Good light. True light. Cant you see it?
WHITE: No. I cant. (35)
Black uses "wheels" and "gears" as a metaphor for the way White's mind is working: It's a machine, sadly grinding out dire conclusions about the human race. White's mind is mechanically condemning itself, along with the rest of the human race. It's like an evil computer in a movie, which has decided that the human race can't be saved.
On the other hand, Black speaks of the "light" in White as a reference to his soul—that underlying "forever thing" (95) which would make his life bearable if he could just get in touch with it. He could forgive himself for whatever he's done (for instance: not visiting his dying father), along with forgiving the rest of humanity, and get on with his life.