The Jews still did not believe that he had been blind and had received his sight until they sent for the man’s parents.
The Jews (or Pharisees) operated off the premise that Jesus did not come from God. He said and did things they didn’t like and that did not agree with the theology they had developed. For them to agree that He had indeed come from God would have necessitated a change on their behalf which they were unwilling to do. Since they believed Jesus did not come from God, He could not have made a miracle, so this miracle must have been faked. Therefore they attempt to prove the falsity of the miracle by the testimony of the man’s parents and then by the man himself.
Interestingly, the Pharisees had passed by this man born blind every day on their way to the Temple and had probably even given him alms (out of a desire to please God and earn their salvation) and yet they had to send for his parents to prove that he was indeed the man who had been blind and begging his entire life. The reason is that they had never really looked at the man. He was just an object to them and not a man in need. They were so wrapped up in their legalistic religion that they had no humanity. God forbid that we should ever lose God’s type of religion for a legalistic, man-made one!