What does John 9:18 mean?

Jesus has miraculously given eyesight to a man born blind (John 9:1–7). This not only fulfills prophecies of the Messiah (Isaiah 29:18; 35:5; 42:7), it also occurred on a Sabbath day (John 9:14), further irritating the religious leaders of Jerusalem.

The gospel of John uses the term "the Jews," in most cases, as a reference to the scribes and Pharisees of Jerusalem. These are the spiritual and religious leaders of the nation of Israel, as well as those who follow their leadership. Here, as in other instances, Jesus' harshest critics and greatest resistance come from the very people who ought to know better.

The fact that this man had always been blind, and was known to be blind, leads to extreme skepticism. The religious leaders of Jerusalem simply refuse to believe that this man has been given sight, so they summon his parents. Their goal is to confirm—or, in their case to hopefully disprove—that this is the same man who was known as a blind-from-birth beggar. The skepticism of these leaders is not entirely unjustified. Their role is to shepherd the people of Israel, and that includes investigating spiritual claims. Where they go wrong is not in asking questions; their error is in taking their skepticism to such extreme levels that they refuse to believe, no matter what.