In John 9, Jesus heals a blind man, which wasn’t unusual for him. He healed lots of blind men in the gospel accounts! But this is the only one recorded by John, and there are a number of things about this miracle that make it special, and point to a meaning much deeper than simply restoring someone’s sight.
The miracle takes place in the context of an argument between Jesus and the religious leaders of the day, ending with the people taking up stones to kill Jesus in the temple. Jesus had made a number of claims about himself and his origin, as well as pointing out the darkness and dishonesty of the people who wanted to discredit him by discounting his testimony and explaining away the signs that he had performed.
So in John 9, Jesus finds a man who is physically blind, sends him to a specific pool called “Sent” and tells him to wash his eyes. That single instruction sets up a chain reaction that fully demonstrates Jesus’ mission in the world, the reception he has received from the leaders, and the opportunity still available for anyone willing to believe his testimony.