What does John 9:28 mean?

In an earlier argument, Jesus pointed out that His religious critics claimed to be followers of Moses, yet failed to act accordingly (John 5:39–47). When Jesus healed a man who had been born blind (John 9:1–7), these same scribes and Pharisees insisted that the miracle was a fraud. They rejected Jesus as a sinner (John 9:16, 24), questioned the healed man (John 9:13), questioned his parents (John 9:18), and brought the beggar back for a second round of interrogation. There, the man pointed out that he'd already answered their questions and sarcastically asked if they'd changed their minds and decided to follow Jesus (John 9:27).

As they did in earlier conversations with Jesus, the scribes and Pharisees respond to these challenges with anger and insults (John 8:41, 48). This verse uses the Greek term loidorēo, which means to "rail at or heap abuses on." This is not an off-hand comment. In this context, it's an act of verbal abuse. For pointing out their prejudice, the once-blind beggar has earned hatred and anger from these educated men.

Once again, the religious leaders stake their claim to religious knowledge. This is the same issue about which they debated Jesus after He healed a crippled man near the Pool of Bethesda (John 5:1–8, 18, 37–47). They refuse to accept any claim contradicting their own traditions and knowledge. In their own minds, there is no possible way in which they could be wrong. Their arrogance will continue in the next verse.