‘And as he passed by he saw a man blind from birth. And his disciples asked him saying, “Rabbi, who did sin, this man or his parents, that he was born blind?”.'
As Jesus was going on His way, He and His disciples saw a man who had been blind from birth. The fact that the disciples knew this suggests that the man was well known, and a kind of landmark. It was something ‘everyone' knew. The fact was general knowledge.
But this time when they saw him it raised a question in the disciples' minds. They had been brought up to believe that misfortune was the result of sin, and that the two were directly linked, (this was certainly central in later Rabbinic thought) so they asked Jesus, ‘Who sinned, this man or his parents, that he was born blind?' Their point here was that the man was born blind, so it was a question of whether he could be seen as guilty at birth, having sinned in the womb, or whether his misfortune should be seen as due to the sins of others. It was a theological question.
Rabbis taught that a babe in the womb could be guilty of its mother's behaviour while bearing him. Thus where a pregnant woman engaged in idolatry her child was also seen as engaging in idolatry. Certainly the Bible does link behaviour as producing judgment and that this sometimes follows a particular sin (see for example Exodus 20:5; Exodus 34:7; Ezekiel 18:4), but it nowhere declares that individual sin can always be directly related to individual misfortune. Indeed the book of Job stresses the opposite. In that book it was the good man who suffered misfortune, and it was his comforters who had been proved to give false advice, who claimed that he suffered because of his sins.
It is significant that when the disciples saw the man the thought does not seem to have crossed their minds that he could be healed. As far as they were concerned the man was an institution. In their view he would always be there like that. Perhaps they thought that as it was a matter of how he was born nothing could be done about it. So the only question that came to their minds was a theological one.