This story raised a lot of questions, but I'd like to focus specifically on some of the questions raised above. I think that, rather than the story being a cyclical piece (though there is evidence of that) it is instead acting much like a graph of exponential increase, which is to say the events become more heightened in their intensity as the story progresses, reaching a peak with the narrator's decision to keep his eyes closed while drawing, as though he has achieved some profound realization. This increase in tension is tied to the narrator discovering more and more about himself, his wife, and Robert the blind man. He realizes something profound may occur after the three of them voraciously inhale their suppers, which is described with very vivid imagery.
The imagery is almost entirely descriptive, as said before; there is little abstraction. This reflects the narrator's tone as a very literal, down-to-earth individual. He is no-nonsense and finds himself literally at a loss when attempting to describe the cathedral to Robert. One of the only moments where his descriptions aren't either of something physical within or outside of him is at the very end, when he says, regarding having his eyes closed, "I thought I'd keep them that way for a little longer. I thought it was something I ought to do." (124) Does this revelation mean that the narrator has transcended the literal interpretation of the world he previously had? By keeping his eyes closed he is blocking one of his most significant portals for sensory exploration and has to rely instead on guesswork, on faith.
Speaking of faith, there are of course multiple references to the blind in the Bible, which may or may not hold significance to "Cathedral." One is reminded in the final pages of the phrase "the blind leading the blind" which becomes rather overt when Robert instructs the narrator to draw a cathedral and leads him, even without the capacity of sight. This would be an ironic inversion of the original intention of the phrase "blind leading the blind" because in this case both parties gain from such leadership: Robert learns what a cathedral looks like (which has obvious religious connotations) and the narrator has a religious experience of self-realization.
A very dense, yet effortless-to-read story.