John Calvin Commentary John 9:30

"The man answered and said unto them, Why, herein is the marvel, that ye know not whence he is, and [yet] he opened mine eyes." — John 9:30 (ASV)

Certainly this is wonderful. He indirectly rebukes them for remaining unmoved by such an illustrious miracle and for pretending that they did not know Christ’s calling; as if he had said, that it was highly improper that such a testimony to Divine power should be disregarded, and that the calling of Christ, so proven and attested, should gain no credibility among them. And, to show their stupidity or malice more clearly, he emphasizes the miracle's excellence by pointing out that, as far as human memory reaches, no one had ever heard of such a thing being done by a man. Therefore, it follows that they are malicious and ungrateful, because they voluntarily shut their eyes to a clear work of God. From this, he infers that Christ was sent by God, because he is endowed with such great power of the Spirit of God, to gain credibility for himself and for his doctrine.