"As he walked along, he saw a man blind from birth. His disciples asked him, ‘Rabbi, who sinned, this man or his parents, that he was born blind?’Jesus answered, ‘Neither this man nor his parents sinned; he was born blind so that God’s works might be revealed in him. We must work the works of him who sent me while it is day; night is coming when no one can work. As long as I am in the world, I am the light of the world.’ When he had said this, he spat on the ground and made mud with the saliva and spread the mud on the man’s eyes, saying to him, ‘Go, wash in the pool of Siloam’ (which means Sent). Then he went and washed and came back able to see. The neighbours and those who had seen him before as a beggar began to ask, ‘Is this not the man who used to sit and beg?’ Some were saying, ‘It is he.’ Others were saying, ‘No, but it is someone like him.’ He kept saying, ‘I am the man.’ But they kept asking him, ‘Then how were your eyes opened?’ He answered, ‘The man called Jesus made mud, spread it on my eyes, and said to me, “Go to Siloam and wash.” Then I went and washed and received my sight.’ They said to him, ‘Where is he?’ He said, ‘I do not know.’"
I have always had trouble with things like congenital birth defects, chronic illness, harm to children, etc. I find the traditional explanation—the fall of man and resulting life of sin—to be mythology.
The idea that blindness, birth defects, etc.—conditions that we, from our limited human perspective, would call negative—are a punishment for "the fall of man" is inconsistent with Jesus's teaching, here and throughout his ministry. His first response is, basically, that neither he nor any of us is qualified to understand the workings of Spirit. Further, he teaches that there is spiritual Good in even the most challenging conditions, if we are willing to allow that Good to express. In this case, the man's blindness allowed Jesus to have a teaching moment. He certainly didn't intend that it be true, but he was willing to be the channel for Spirit.