John Chrysostom
But if He came not to judge the world, how is it that the unbeliever "is judged already," when the time of judgment has not yet come?
He says this either because unbelief without repentance is in itself the greatest torment, or else He is foretelling the future.
A murderer, even if he has not been condemned by a judge's sentence, is already condemned by the very character of his deed. So it is with the unbeliever.
Adam died on the very day when he tasted of the tree. Such was the decree: "In the day that you eat of it, you shall surely die" (Gen 2:17). Yet he lived after that.
How then did he die? Both by God's decree and by the character of his deed.
Whoever has made himself liable to punishment is under punishment, even if not yet in fact, but by decree.
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So that no one, hearing "He came not to judge the world," might think that he can sin with impunity, and so become still more careless, Christ forestalls such negligence by saying: "He is judged already."
Since there will be a judgment, but it has not yet come, He immediately stirs up fear of torment and already shows the punishment.
This also proves God's great love for mankind: God not only gave His Son, but also postponed the time of judgment. Thus those who sinned and did not believe might have the possibility of cleansing their sins.
"He who believes in Him is not judged": he who believes in the Son, and does not subject Him to scrutiny; he who believes, and does not pry.
But what if one who believes has an unclean life and evil works? Paul does not call such people true believers: "They say that they know God, but by their works they deny Him" (Tit 1:16).
Here, however, Christ says that they are liable to condemnation not for unbelief, but will undergo the harshest punishment for their works. They are not punished for unbelief, because they have already believed.