Another possibility would be to focus on the need/benefits of learning to see ourselves, others, and the world we live in from more than one perspective. At the heart of this story is the narrator's transformation from being completely self-absorbed and incapable of seeing things from another point of view to being open to those possibilities.
I would focus on the need for tolerance and acceptance/understanding of others who are different than we are...
Through the forging of relationships our "blindness" can be enlightened. In Cathedral we can recognize the emotional blindness and the isolation of ourselves from other cultures and ideologies can create more of a inability to see truth than is created through physical blindness.
What about making a statement about the importance of communion with another human being? There are so many works to which you can refer--any work in which friendship or love is a theme. ("Silas Marner," "Jane Eyre," "Dr. Zhivago," etc.. Joseph Conrad, author of the short story "Secret Sharer" writes about the isolation of humans and their need to share.) Meaning in life depends upon sharing.
In "Cathedral" when the narrator draws with his eyes closed, sharing the movement of the pencil as he traces the lines with Robert's hand on his, he senses this meaning of sharing, this communion of two souls/minds.