13 “And this is the judgment, that light has come into the world, and men loved darkness rather than light, because their deeds were evil.” My brethren, whose works does the Lord find to be good? The works of none: He finds the works of all evil. How is it, then, that some have done the truth, and have come to the light? For this is what follows: “But he that does truth comes to the light, that his deeds may be made manifest, that they are wrought in God.” In what way have some done a good work to come to the light, namely, to Christ?
And how have some loved darkness? For if He finds all men sinners, and heals all of sin, and that serpent in which the Lord's death was figured healed them that were bitten, and on account of the serpent's bite the serpent was set up, namely, the Lord's death on account of mortal men, whom He finds unrighteous; how are we to understand that “this is the judgment, that light has come into the world, and men loved darkness rather than light, because their deeds were evil”? How is this?
Whose works, in fact, are good? Have You not come to justify the ungodly? “But they loved,” says He, “darkness rather than light.” There He laid the emphasis: for many loved their sins; many confessed their sins; and he who confesses his sins, and accuses them, does now work with God. God accuses your sins: and if you also accuse, you are united to God. There are, as it were, two things, man and sinner. That you are called man, is God's doing; that you are called sinner, is man's own doing.
Blot out what you have done, that God may save what He has done. It behooves you to hate your own work in you, and to love the work of God in you. And when your own deeds will begin to displease you, from that time your good works begin, as you find fault with your evil works. The confession of evil works is the beginning of good works. You do the truth, and come to the light. How is it you do the truth? Thou dost not caress, nor soothe, nor flatter yourself; nor say, “I am righteous,” while you are unrighteous: thus, you begin to do the truth.
You come to the light, that your works may be made manifest that they are wrought in God; for your sin, the very thing that has given you displeasure, would not have displeased you, if God did not shine into you, and His truth show it you. But he that loves his sins, even after being admonished, hates the light admonishing him, and flees from it, that his works which he loves may not be proved to be evil. But he that does truth accuses his evil works in himself, spares not himself, forgives not himself, that God may forgive him: for that which he desires God to forgive, he himself acknowledges, and he comes to the light; to which he is thankful for showing him what he should hate in himself.
He says to God, “Turn away Your face from my sins:” yet with what countenance says it, unless he adds, “For I acknowledge mine iniquity, and my sin is ever before me?” Be that before yourself which you desire not to be before God. But if you will put your sin behind you, God will thrust it back before your eyes; and this He will do at a time when there will be no more fruit of repentance.
Source: Tractates on the Gospel of John (New Advent)