In this story, the blind man is the one who can truly "see", or who really understands how life can be beautiful, meaningful, and happy, whereas the narrator is the one who is "blind" to those things. The narrator spends the entire time moaning and groaning about life, his wife, the blind man, and his station in life, and it isn't until the very end, when he closes his eyes and guides the blind man's hands, that he truly sees and feels a profound experience that makes him grateful and happy. The narrator, a very sarcastic and bitter man, feels, as he closes his eyes to attempt to draw a cathedral for a blind man, that "it was like nothing else in my life up to now." That's a pretty strong statement for him, considering how negative he's been in the story up to this point. He has to let go of the senses that he has clung to for so long, and in the dark, have a leap of faith as he drew the cathedral. He put himself in someone else's shoes, something that he probably has never even tried before. Before this, he was a bit resentful of the blind man coming to visit, resentful of the company, his wife's fondness for the man, and the inconvenience the visit put on his life. He was thinking only from his own perspective-not from the blind man's, or his wife's. But, as he closes his eyes and draws, he sees life from another person's perspective, and finds it incredible. It is a profound moment for him. So, the blind man led the seeing man to truly see something for the first time in his life. The blind man reveals the petty, selfish nature of the narrator, and then helps him to have an experience that will hopefully help to change that character. Blindness helps to reveal Robert as the truly seeing, wise one, that guides the storyteller to new and positive experiences.
Those are just some thoughts along those lines; I hope that they help get you started. Good luck!