The fact that smoke obscures vision even for the sighted is of course important; the cigarettes being smoked not only make Robert more like the unnamed narrator, but they also make the narrator more like the bind Robert by reducing this narrator's vision, though not in an extreme way. The smoke that uncurls between these two characters later in the story is even more effective at bringing them together. The trio of Robert, wife, and narrator turn from alcohol and tobacco to cannabis when the narrator rolls two joints to smoke and engages Robert in his first try of the substance. It is under the influence of this drug, and perhaps of Robert's presence and spirit, that a true transformation takes place both between Robert and the narrator and within the narrator himself. The two go from watching (or listening to) a television...

It took smoke to obscure his vision and perception enough to begin to open up, and with his eyes closed the transformation becomes complete. Smoke is truly a powerful symbol here, acting as an impetus and marker for the inner action that makes up the story.
Works Cited

Carver, Raymond. "The Cathedral. Accessed 18 October 2012.

http://nbu.bg/webs/amb/american/6/carver/cathedral.htm

McCaffrey, Larry and Gregory, Sinda. "An Interview with Raymond Carver." Mississippi

Review 14(1/2): 62-82.