John Calvin Commentary John 9:17

"They say therefore unto the blind man again, What sayest thou of him, in that he opened thine eyes? And he said, He is a prophet." — John 9:17 (ASV)

They say to him who had been blind. The more diligently they inquire, the more impressively the truth of God appears, for they act as if someone were trying to extinguish a strong flame with their breath. Thus, when we see wicked men scheme to do all they can to crush the truth of God, we have no reason to be afraid or overly anxious about the outcome, because all they will achieve by this will be to make its light burn even brighter.

What sayest thou of him? When they ask the blind man for his opinion, they do so not because they wish to abide by his judgment or place any value on it, but because they hope that the man, struck with fear, would reply as they wished. In this respect, the Lord disappoints them. For when a poor man disregards their threats and boldly maintains that Christ is a Prophet, we ought rightly to ascribe it to the grace of God, so this boldness is another miracle.

And if he so boldly and freely acknowledged Christ to be a Prophet, though he did not yet know that the Lord Jesus was the Son of God, how shameful is the treachery of those who, subdued by fear, either deny him or are silent about him, though they know that he sits at the right hand of the Father and that he will come from there to be the Judge of the whole world! Since this blind man did not quench a small spark of knowledge, we ought to strive that an open and full confession may blaze forth from the full brightness that has shone into our hearts.