Isaiah wrote about restoring the sight of the blind as part of the Messiah’s ability…And the Lord said:
— Isaiah 29:18 In that day the deaf will hear words read from a book,
and the blind will see through the gloom and darkness.
— 35:5 And when he comes, he will open the eyes of the blind and unplug the ears of the deaf.
— 42:7 You will open the eyes of the blind. You will free the captives from prison, releasing those who sit in dark dungeons.
Jesus speaks to his disciples in a third party-like conversation about the cause of blindness and Him being the Light of the world. That’s a Messianic claim! Then He physically takes direct action by coating over the man’s eyes with clay he’s just made. The mixing of the mud is evidence of “violation” of working on the Sabbath! He never tells the blind man his sight is going to miraculously be restored. The blind man must choose to risk responding to Jesus and go to the pool to wash. That’s a step of faith!
The sticking point for the Pharisees was complicated. Twice Jesus had confronted the Pharisees hypocrisy [John 7:23 and Matthew 12:5]. Jewish rules had legitimate provisions for violating the Sabbath in specific cases like circumcision in order to obey Mosaic law, temple service or the birth of a baby. Isaiah’s words, a broken rule, the eyes of a blind man being opened and an itinerant rabbi who claimed to be the Light of the world became their sticking point. Isaiah’s words were a trusted part of the Pharisees Messianic history and according to their own rules denying a miracle of God was unbelief. The evidence of acknowledging this miracle might prove Jesus to be the Lord Isaiah wrote about. That didn’t mesh with what they’d carefully mapped out for the coming Messiah. They couldn’t risk choosing to take that next step of faith.