The religious leaders are stumped. They can't explain Jesus' power, so they resort to insults. But this man, newly sighted, has a clear line of reasoning.
In John 9:30, the man directly confronts the religious leaders with a simple, powerful logic. He highlights the stark contrast between their supposed knowledge and his undeniable experience.
Their Ignorance vs. His Experience
The leaders claim they don't know Jesus' origin or authority ('we know not whence he is,' John 9:29). Yet, this man, who was born blind, has had his eyes opened by Jesus. This isn't a matter of theological debate for him; it's a lived reality. The miracle is the irrefutable proof that Jesus' power is from God, something the learned leaders ought to recognize but refuse to.
The 'Marvel' of Their Blindness
He calls it a 'marvel'—not that Jesus healed him, but that they, the supposed experts on God's work, are blind to the obvious implications of such a miracle. Their intellectual blindness, despite all their knowledge, is the true marvel to him.