8 See John himself observing humility. Assuredly he was a righteous and a great man, who from the Lord's bosom drank in the secrets of His mysteries; he, the man who by drinking from the Lord's bosom indited of His Godhead, “In the beginning was the Word, and the Word was with God:” he, being such a man as this, says not, You have an advocate with the Father; but, “If any man sin, an advocate,” says he, “have we.” He says not, you have; nor says, you have me; nor says, you have Christ Himself: but he puts Christ, not himself, and says, also, “We have,” not, you have. He chose rather to put himself in the number of sinners that he might have Christ for his advocate, than to put himself in Christ's stead as advocate, and to be found among the proud that shall be condemned. Brethren, Jesus Christ the righteous, even Him have we for our advocate with the Father; “He,” even He, “is the propitiation for our sins.” This whoso has held fast, has made no heresy; this whoso has held fast, has made no schism. For whence came schisms? When men say, “we” are righteous, when men say, “we” sanctify the unclean, “we” justify the ungodly; “we” ask, “we” obtain. But what says John? “And if any man sin, we have an advocate with the Father, Jesus Christ the righteous.” But some man will say: then do the saints not ask for us? Then do bishops and rulers not ask for the people? Yea, but mark the Scriptures, and see that rulers also commend themselves to the prayers of the people. Thus the apostle says to the congregation, “Praying withal for us also.” The apostle prays for the people, the people prays for the apostle. We pray for you, brethren: but do ye also pray for us. Let all the members pray one for another; let the Head intercede for all. Therefore it is no marvel that he here goes on and shuts the mouths of them that divide the Church of God. For he that has said, “We have Jesus Christ the righteous, and He is the propitiation for our sins:” having an eye to those who would divide themselves, and would say, “Lo, here is Christ, lo, there;” and would show Him in a part who bought the whole and possesses the whole, he immediately goes on to say, “Not our sins only, but also the sins of the whole world.” What is this, brethren? Certainly “we have found it in the fields of the woods,” we have found the Church in all nations. Behold, Christ “is the propitiation for our sins; not ours only, but also the sins of the whole world.” Behold, you have the Church throughout the whole world; do not follow false justifiers who in truth are cutters off. Be in that mountain which has filled the whole earth: because “Christ is the propitiation for our sins; not only ours, but also the sins of the whole world,” which He has bought with His blood.
9. “And in this,” says he, “we do know Him, if we keep His commandments.” What commandments? “He that says, I know Him, and keeps not His commandments, is a liar, and the truth is not in him.” But still you ask, What commandments? “But whoso,” says he, “keeps His word, in him verily is the love of God perfected.” Let us see whether this same commandment be not called love. For we were asking, what commandments, and he says, “But whoso keeps His word, in him verily is the love of God perfected.” Mark the Gospel, whether this be not the commandment: “A new commandment,” says the Lord, “give I unto you, that you love one another. — In this we know that we are in Him, if in Him we be perfected.” Perfected in love, he calls them: what is perfection of love? To love even enemies, and love them for this end, that they may be brethren. For not a carnal love ought ours to be. To wish a man temporal good, is good; but though that fail, let the soul be safe. Do you wish life to any that is your friend? You do well. Do you rejoice at the death of your enemy? You do badly. But haply both to your friend the life you wish him is not for his good, and to your enemy the death you rejoice at has been for his good. It is uncertain whether this present life be profitable to any man or unprofitable: but the life which is with God without doubt is profitable. So love your enemies as to wish them to become your brethren; so love your enemies as that they may be called into your fellowship. For so loved He who, hanging on the cross, said, “Father, forgive them, for they know not what they do.” For he did not say, Father let them live long, me indeed they kill, but let them live. He was casting out from them the death which is for ever and ever, by His most merciful prayer, and by His most surpassing might. Many of them believed, and the shedding of the blood of Christ was forgiven them. At first they shed it while they raged; now they drank it while they believed. “In this we know that we are in Him, if in Him we be made perfect.” Touching the very perfection of love of enemies, the Lord admonishing, says, “Be therefore perfect, as your Heavenly Father is perfect. He,” therefore, “that says he abides in Him, ought himself also so to walk, even as He walked.” How, brethren? What does he advise us? “He that says he abides in Him,” i.e., in Christ, “ought himself also so to walk even as He walked.” Haply the advice is this, that we should walk on the sea? That be far from us! It is this then, that we walk in the way of righteousness. In what way? I have already mentioned it. He was fixed upon the cross, and yet was He walking in this very way: this way is the way of charity, “Father, forgive them, for they know not what they do.” If, therefore, you have learned to pray for your enemy, you walk in the way of the Lord.
10. “Dearly beloved, I write unto you no new commandment, but the old commandment which you had from the beginning.” What commandment calls he “old? Which you had,” says he, “from the beginning. Old” then, in this regard, that you have already heard it: otherwise he will contradict the Lord, where He says, “A new commandment give I unto you, that you love one another.” But why an “old” commandment? Not as pertaining to the old man. But why? “Which you had from the beginning. The old commandment is the word which you have heard.” Old then, in this regard, that you have already heard it. And the selfsame he shows to be new, saying, “Again, a new commandment write I unto you.” Not another, but the selfsame which he has called old, the same is also new. Why? “Which thing is true in Him and in you.” Why old, you have already heard: i.e., because you knew it already. But why new? “Because the darkness is past, and the true light now shines.” Lo, whence it is new: because the darkness pertains to the old man, but the light to the new man. What says the Apostle Paul? “Put off the old man, and put on the new.” And again what says he? “You were sometime darkness, but now light in the Lord.”
Source: Homilies on the First Epistle of John (New Advent)