18 But the Jews did not believe concerning him, that he had been blind and received his sight, until they called the parents of him who had received his sight.
19 And they asked them, saying, “Is this your son, who you say was born blind? How then does he now see?”
20 His parents answered them and said, “We know that this is our son, and that he was born blind;
21 but by what means he now sees we do not know, or who opened his eyes we do not know. He is of age; ask him. He will speak for himself.”
22 His parents said these things because they feared the Jews, for the Jews had agreed already that if anyone confessed that He was Christ, he would be put out of the synagogue.
23 Therefore his parents said, “He is of age; ask him.”
The man's parents pointed out that their son was of age (v. 21). so they wouldn't be held responsible for him. They were afraid of being thrown oout of the synagogue, a fear their son no longer had.
who ye say was born blind (v. 19) — as though they had been lying his entire life.
The man might have expected his parents to be happy he had been healed, or at least back up his story, but out of fear, they did neither.
The Greek expression for "be put out of the synagogue" states an action similar to excommunication. The expression is uniquely Johannine (used here and in 12:42; 16:2). According to Jewish regulations, there were two kinds of excommunication: one that would last for thirty days until the offender was reconciled, and one that was a permanent "ban" accompanied by a curse. In a tight-knit community, it was a terrible judgment to be removed from the synagogue, the very center of Jewish life. Many Jews in John's day had been "de-synagogued" because they confessed Jesus to be the Christ. An ancient document called the Cairo Genizah (c. A.D. 80-90) contains a curse against the Nazarenes, banning them from participating in the synagogue. Perhaps John included this story for particular encouragement to those Christians who were experiencing such treatment. — Opening the Gospel of John, by Philip W. Comfort and Wendell C. Hawley, page 159