As Jesus and his disciples are walking along, they come across a blind man.
This word shows that the author is about to describe a new event. (See: rc://en/ta/man/translate/writing-newevent)
as Jesus passed by
Here "Jesus" is a synecdoche for Jesus and the disciples. AT: "as Jesus and his disciples passed by" (See: rc://en/ta/man/translate/figs-synecdoche)
who sinned, this man or his parents ... blind?
This question reflects the ancient Jewish belief that sin caused all illnesses and other deformities. The rabbis also taught that it was possible for a baby to sin while still in the womb. AT: "Teacher, we know that sin causes a person to be blind. Whose sin caused this man to be born blind? did this man himself sin, or was it his parents who sinned?" (See: rc://en/ta/man/translate/figs-explicit)