This is probably the most challenging aspect of Raymond Carver's short story, "Cathedral:" why does Robert have the narrator draw a picture of the cathedral shown on the television?
The narrator is particularly uncharitable in his assessment of Robert, his wife's blind friend who comes to visit after his wife dies. The narrator seems jealous and childish. When the man arrives, the narrator looks out the window for his first view, and says:
She went around to the other side of the car to where the blind man was already starting to get out. This blind man, feature this, he was wearing a full beard! A beard on a blind man! Too much, I say.
Perhaps part of the difficulty is that the narrator does not know how to act with a victim of disability. He says to his wife:
“I don’t have any blind friends,” I said.
Her curt response to him is:
“You don’t have any friends,” she said. “Period..."
It is only when dinner is over and the narrator brings out some marijuana to smoke that he relaxes. He offers some to Robert, who tries it—a new experience for him. What also may aid in the narrator's ability to more easily connect with Robert is the blind man's affability—whatever the narrator says or does, Robert does not take it personally.
When they begin to "watch" TV, Robert asks the narrator to describe what he sees. The narrator struggles, even apologetic, that he can't do a better job putting into words the images before him. Robert suggests that he get some "heavy paper" and a pen, and draw.
“Go ahead, bub, draw,” he said. “Draw. You’ll see. I’ll follow along with you. It’ll be okay. Just begin now like I’m telling you. You’ll see. Draw,” the blind man said.
Robert is extremely supportive—full of encouragement.
“Swell,” he said. “Terrific. You’re doing fine,” he said.
The narrator's antagonism dissipates. By following the movement of the narrator's hand as he draws, and feeling the paper, Robert is able to gain some insight as to the shape of the cathedral.
The benefits of this activity may be threefold. First, the narrator's inability to articulate what he sees may provide him a context with which to understand Robert's inability to see: both are at a disadvantage—both have a "handicap." Second, the project creates a common purpose and a bond between the men who have the same goal: to draw the cathedral.
The blind man said, “We’re drawing a cathedral. Me and him are working on it..."
Something that strikes me is that Robert is often referred to as "the blind man," so I cannot help but feel that the concept of "the inability to see" is key, but not just for Robert—it is also the case for the narrator who cannot see the value of Robert simply because he may be jealous of the man's friendship with his wife, and/or because he perceives Robert as less than adequate because of his blindness.
Finally, the "cathedral" itself may well introduce the idea of a "miracle." It certainly seems to be just that when the narrator is so taken by the exercise that his perceptions change. In finding a way to "see" Robert differently, the narrator may well be able to see his own life differently—in a much more positive way.