A good thesis for Raymond Carver's "Cathedral" can be that a person can share meaningful experiences with those from whom he least expects anything.
The narrator, the husband of a sensitive woman, is a man who has a purposeless existence. He is disconnected from his wife, disinterested...
in most things, and suffering from an existential angst. He is less than thrilled--jealous, in fact--that his wife has invited to their home her blind friend, Robert. As he listens to his wife talk to Robert, he has resentment that she can speak of feelings and share with her friend things that she has not even mentioned to him.
After his wife goes on to bed, the narrator and Robert stay in the room where the television is, and they smoke some cannabis. When Robert asks the narrator to draw a cathedral that is being described by the speaker of the television program they are watching, the narrator finds a brown paper bag on which they can draw with Robert keeping his hand on top of that of the narrator. This act of creation becomes a meaningful spiritual experience for the two men, and the trust and friendship shown to him by Robert gives the narrator a new meaning to his life.
“Well?” [Robert] said. “Are you looking?” My eyes were still closed. I was in my house. I knew that. But I didn’t feel like I was inside anything. “It’s really something,” I said.
For the first time, the narrator feels things, spiritual things, and he has had a meaningful experience.