At first sight it is an ordinary everyday story which shows common relations between ordinary people. But if you try to look deeper into the story and find out the main idea of it you will understand that Robert Carver shows a miserable blindness of a sighted person whom the congenitally blind gives the insight.
The narrator of the short story Cathedral is at the same time the main character of the story whose life conception is at so low level that it is easy to see his inner emptiness.
In order to prove this statement I'd like to add the fact that the narrator's speech consists of many short simple sentences which are so dull and without any brightness. He even does not use epithets to make his speech more vivid. (Runyon) He need not it. He does not give a full description of his house because he need not it. He can not give a portrait of his wife. The only description the narrator gives in the story is the description of the cathedral which Robert asked him to do. He said: "I stared hard at the shot of the cathedral on the TV. How could I even begin to describe it?" (Carver) But he failed to do it saying "I'm just no good at all". He explains this fact to Robert saying that he has no any feelings to it.
All the facts we can learn from the narrator's story are based on complete annoyance. When the narrator learns that his wife invited the blind to visit her he becomes nervous: "My idea of blindness came from the movies. In the movies the blind moved slowly and never laughed... A blind man in my house was not something I looked forward to". (Carver) He was surprised that Robert did not use glasses and did not have a stick. Moreover he had a well-tended beard which gave his appearance an intelligent look.
The other very important thing is that the author did not give any name to the narrator as well as to his wife. The only person who has a name in the story is Robert, the congenitally blind man, who is not only sensitive and kind-hearted but also a strong-willed man. (Kleppe, Miltner)
Raymond Carver used different ways to put together these two men in the story Cathedral - the "blind" narrator and the "sighted" blind Robert. But the moment when the wife falls asleep on the coach in the room and two men (her husband and Robert) stay alone, plays a very important role in the literary work. It is this very moment which will help the narrator to feel the beauty of the cathedral he will draw by means of Robert's hand. The narrator with his eyes closed cannot see anything, he can only feel as well as the blind. And his exclamation proves that he likes it: "It's really something". (Carver)
Another episode which helps the readers to see the shallow-branded nature of the narrator is given by the author at the beginning of the story - the episode with tapes. When the narrator learns from his wife that she has a correspondence with the blind whom she regularly sends the recordings of her voice he shows his ambivalence. He does not understand her gladness and pleasure. (Nesset) Moreover he does not like the way his wife tells the blind man whom he has never seen before the exact details of her life including his own personality. He understands that the blind man is a real friend of his wife. She likes him and she does not want to stop their relations. The narrator himself does not have any friends, he is alone. His wife is the only dear person in his life. Nevertheless she loves him. She married him and it was her own decision. The main problem of the narrator lies within his own personality and the author tries to let the readers see it throughout the story. (Esch., On Raymond's Carver Cathedral)
One more fact in the story that shows the blindness of the narrator and the shallowness of his nature is his addiction to the alcohol and marihuana as well as the orgy of eating. Instead of switching the conversation off to some beautiful thing and to discuss the beauty of the nature around or some interesting events in the country, or some catching book, or newspaper article, everything that is interesting for him is drinking and eating and smoking marihuana. He uses all these things to get the sense of satisfaction. It is his symbol of lack. (Lacan) The "blind" narrator cannot see the beauty and has no any skills in talk. It is beyond his abilities. And the blind man shows a good example of a true husband who spends the last days of his wife near her in the hospital "sitting beside the bed and holding her hand". (Carver) The dearest people are closer to Robert than any drugs and alcohol.
In conclusion I should say that Raymond Carver could show his readers in his story Cathedral not only the true human relations by the example of the blind man Robert, but also shallowness and ignorance, jealousy and inhumanity by the example of the narrator whom he even did not give a name in his literary work. Robert has a physical blindness but he has an ability of understanding people.
The blind man is older than narrator and he knows how to help such an ignorant person to feel and to understand his own world, the world of the blind which is build on the feelings and emotions.
Moreover the blind man is merciful to his wife's and other people's feelings, what cannot be said about the narrator.
Both men, the blind and the narrator can understand each other. Robert can feel and imagine the cathedral by means of the narrator and the narrator can feel what the blind feel by means of Robert.
At the end of the story the author proves the readers that even such a miserable person as a narrator have a chance to change his outlook on life which is very important for him.
I think that the blindness draw the line between the narrator and the blind man at the beginning of the story Cathedral and unites these two completely different men at the end. Robert helps the narrator to get the insight.