From The Good and Beautiful God by James Bryant Smith:
Jesus encountered a man who was born blind, and was asked a question by his disciples, “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.” (John 9:2,3) Jesus was making it clear that there is no correlation between someone’s sin and his infirmity. Instead Jesus healed the man. If he believed that the man’s blindness was a fair and just punishment for his sins he could have walked away. Instead Jesus healed the blind man and so revealed the power of God.
Merrill Tenney concludes, “Jesus refused to accept either alternative suggested by the disciples’ question. He looked on the man’s plight, not as retribution for some offense committed either by his parents or himself, but as an opportunity to do God’s work. Jesus did not consider the blindness as punishment or as a matter of irrational chance; it was a challenge to manifest God’s healing power in the man’s life.”