7 It requires great labor in this world, brethren to get clear of the vice which the Lord has noted in this place, so as not to judge by appearance, but to keep right judgment. The Lord, indeed, admonished the Jews, but He warned us also; them He convicted, us He instructed; them He reproved, us He encouraged. Let us not imagine that this was not said to us, simply because we were not there at that time. It was written, it is read; when it was recited we heard it; but we heard it as said to the Jews; let us not place ourselves behind ourselves and watch Him reproving enemies, while we ourselves do that which the truth may reprove in us.
The Jews indeed judged by appearance, but for that reason they belong not to the New Testament, they have not the kingdom of heaven in Christ, nor are joined to the society of the holy angels; they sought earthly things of the Lord; for a land of promise, victory over enemies, fruitfulness of child-bearing, increase of children, abundance of fruit—all which things were indeed promised to them by God, the True and the Good, promised to them, however, as unto carnal men,— all these things made for them the Old Testament.
What is the Old Testament? The inheritance, as it were, belonging to the old man. We have been renewed, have been made a new man, because He who is the new man has come. What is so new as to be born of a virgin? Therefore, because there was not in Him what instruction might renew, because He had no sin, there was given Him a new origin of birth. In Him a new birth, in us a new man. What is a new man? A man renewed from oldness. Renewed unto what? Unto desiring heavenly things, unto longing for things eternal, unto earnestly seeking the country which is above and fears no foe, where we do not lose a friend nor fear an enemy; where we live with good affection, without any want; where no longer any advances, because none fails; where no man is born, because no man dies; where there is no hungering nor thirsting; where immortality is fullness, and truth our aliment.
Having these promises, and pertaining to the New Testament, and being made heirs of a new inheritance, and co-heirs of the Lord Himself, we have a far different hope from theirs: let us not judge by appearance, but hold right judgment.
Source: Tractates on the Gospel of John (New Advent)