John 3:19

This is the judgment, &c. (Vulg.) Judgment, i.e., cause of judgment, or condemnation. This is the cause why those are already condemned who believe not on Me, because they have preferred darkness, and ignorance of God, and of what they ought to do, and their own pleasures and lusts and sins upon the earth, rather than light, that is, Christ, who hath brought the knowledge of God and salvation into the world. For light and darkness are the symbols of these things. Wherefore Bede says, He calls Himself the Light; sins He calls darkness. Moreover, light came into the world to arouse men, says the Gloss: to admonish them to know their evils, says S. Chrysostom. "For they themselves would not admit the light of truth and holiness, which He preached by His word and example." In like manner many at the present day become heretics that they may follow their carnal will, which heresy permits, but the faith forbids. Therefore to convert a heretic make use of this method: first persuade him to lead an honest life, moral, chaste, and holy. Thus will you the more easily bring him to the true faith.

2. Judgment might be taken thus, as signifying the condemnation and rejection of unbelievers, or the judgment wherewith they condemn themselves, in that they prefer darkness to light, that is, cupidity to sanctity, ignorance to knowledge, the devil to God. Wherefore Christ as it were says to such, "It is not I who judge thee, but thine own conscience which judges and condemns thee."