It is clear that the first person point of view selected is a rather interesting choice for this excellent story. However, I think that deliberately choosing to tell the story through perhaps the most unsympathetic character, the husband who appears to be deliberately rude to both his wife and his guest, we see the transformation that the guest manages to bring about in the character of the narrator that much more clearly because of his earlier rudeness.
As the story begins, we see that even though Robert has just lost his wife, the narrator is still rude about the way that he feels threatened by the invasion of his personal space. He crassly jokes about taking Robert bowling, and when Robert comes draws attention to his blindness by asking questions such as which side of the train he sat on in his journey and then pointedly turns on the TV when conversation runs dry.
However, in spite of this, it is clear that the narrator's conversation with Robert, especially when he is asked to draw a cathedral so that Robert can "see" what they look like, has a big impact on him, triggering an epiphany as the narrator chooses to keep his eyes closed even when Robert tells him to open them:
But I had my eyes closed. I thought I'd keep them that way for a little longer. I thought it was something I ought to do... My eyes were still closed. I was in my house. I knew that. But I didn't feel like I was inside anything.
The narrator for perhaps the first time in his life is able to empathise with another human being, and his experience of blindness, albeit temporary, is actually something that is very liberating for him. To have the story narrated from this character's point of view allows us to appreciate and understand the massive change that the narrator experiences through meeting Robert.