Religious imagery
The novel/play is filled with religious imagery. The white professor wonders if the black man who saved him from the train station is an angel who was sent to him. Therefore, the white professor contradicts himself right from the start, because the reason he wants to end his life is that he doesn't believe in anything. The black man is a believer who is convinced he heard the words of God when he needed it the most. There is a considerable discussion about the Bible and religion in general and what makes a person believe or not believe.
The Room
The room is the only setting of the novel/play. The two of them are sitting in the black man's room which doesn't hold any valuable possessions aside from what's necessary. The reason for that is that the black man provides shelter for homeless and drug abusers so there is no point having anything of value because it will be gone before he knows it.