This excellent story by Carver contains many symbols, but I will just pick two of the most obvious ones to my mind. Firstly, and perhaps most blatant, is the symbol of the cathedral that the narrator draws with the blind man who is his guest holding on to his hands. In his attempts to describe what a cathedral is to Robert, the narrator literally finds that words fail him. However, as they talk about cathedrals, it is clear that they are linked with some kind of belief in something bigger, greater and beyond ourselves. Note how the narrator responds to Robert's question about if he is religious:
I said, "The truth is, cathedrals don't mean anything special to me. Nothing. Cathedrals. They're something to look at on late-night TV. That's all they are."
Of course, by the end of the short story, we see that the narrator, through trying to draw a cathedral with his eyes closed, has perhaps rediscovered some sort of belief in something beyond himself.
Secondly, the blind man, Robert, introduces us to the second symbol of this short story, which is of course blindness. What is particularly interesting is how at the end of the story, after being invited to close his eyes and draw by Robert, the narrator chooses to keep his eyes closed. Note his response to this:
My eyes were still closed. I was in my house. I knew that. But I didn't feel like I was inside anything.
Being "blind" is actually shown as a way of "seeing" more truly and insightfully than mere sight allows. Robert, through encouraging the narrator to draw with his eyes shut, makes him see the truth of this statement, until at the end, the narrator voluntarily chooses to keep his eyes shut. He discovers how sight can be gained paradoxically through blindness, and as a result, he experiences a great feeling of liberation and freedom.