17 By these words, then, were “some of the Pharisees” disturbed, “and said unto Him, Are we blind also?” Hear now what it is that moved them, “And they who see may be made blind.” “Jesus said unto them, If you were blind, you should have no sin;” while blindness itself is sin. “If you were blind,” that is, if you considered yourselves blind, if you called yourselves blind, you also would have recourse to the physician: “if” then in this way “you were blind, you should have no sin;” for I have come to take away sin.
“But now ye say, We see; [therefore] your sin remains.” Wherefore? Because by saying, “We see:” ye seek not the physician, you remain in your blindness. This, then, is that which a little above we did not understand, when He said, “I have come, that they who see not may see;” for what means this, “that they who see not may see”? They who acknowledge that they do not see, and seek the physician, that they may receive sight. And “they who see may be made blind:” what means this, “they who see may be made blind”?
That they who think they see, and seek not the physician, may abide in their blindness. Such discerning therefore of one from another He called judgment, when He said, “For judgment I have come into this world,” whereby He distinguishes the cause of those who believe and make confession from the proud, who think they see, and are therefore the more grievously blinded: just as the sinner, making confession, and seeking the physician, said to Him, “Judge me, O God, and discern my cause against the unholy nation,” — namely, those who say, “We see,” and their sin remains.
But it was not that judgment He now brought into the world, whereby in the end of the world He shall judge the living and the dead. For in respect to this He had said, “I judge no man;” seeing that He came the first time, “not to judge the world, but that the world through Him might be saved.”
Source: Tractates on the Gospel of John (New Advent)