This is my commandment, that you love one another, as I have loved you.

“(Tract. lxxxiii. 3) Where then love is, what can be wanting? where it is not, what can profit? But this love is distinguished from men’s love to each other as men, by adding, As I have loved you. To what end did Christ love us, but that we should reign with Him? Let us therefore so love one another, as that our love be different from that of other men; who do not love one another, to the end that God may be loved, because they do not really love at all. They who love one another for the sake of having God within them, they truly love one another.”

“(Hom. xxvii. in Evang.) But when all our Lord’s sacred discourses are full of His commandments, why does He give this special commandment respecting love, if it is not that every commandment teaches love, and all precepts are one? Love and love only is the fulfilment of every thing that is enjoined. As all the boughs of a tree proceed from one root, so all the virtues are produced from one love: nor hath the branch, i. e. the good work, any life, except it abide in the root of love.”

“Above, the Lord admonished his disciples to abide in him; here he shows what it is to abide in him, and this in three ways. First, that to abide in him is to abide in his love; second, he shows that to keep his commandments is to abide in his love, at the place, "if you keep my commandments, you shall abide in my love"; third, he shows that the observance of charity is his commandment, at the place, "this is my commandment," etc. Concerning the first he does two things. First he recalls the benefit conferred on the disciples; second he exhorts them to persevere, at the place, "abide in my love." He says therefore first, that this — namely, that we abide in Christ — is from his grace; and this grace is indeed the effect of his own love, Jeremiah 31:3: "I have loved you with an everlasting love." From which it is clear that all our good works are ours to us from the benefit of divine love. For they would not be ours, except because faith works through love; nor would we love, unless we were first loved. And therefore, recalling this benefit, he said, "as the Father has loved me, I also have loved you." But it should be noted that the word "as" sometimes denotes equality of nature, but sometimes a likeness of action. The Arians, however, erring, wanted the word "as" to import equality, and by this — as has often been expressed above — they concluded that he was less than the Father. But this is false; and therefore, according to Augustine, it must be said that the word "as" expresses a likeness of grace and of love: for the love with which the Son loves the disciples is a certain likeness of that love with which the Father loves the Son. For since to love someone is to will good to him, the Father loves the Son according to the divine nature, insofar as he wills for him his own infinite good, which he himself has, by communicating to him the very same nature, numerically, which he himself has; above, John 5:20: "the Father loves the Son, and shows him all things which he himself does." He also loves him according to the human nature; Hosea 11:1: "Israel was a child, and I loved him, and out of Egypt I called my son." And this, namely, so that he might be at once God and man. And to none of these did the Son love the disciples, for neither did he love them to this end, that they should be God by nature, nor that they should be united to God in person; but he loved them unto a certain likeness of these, namely, that they should be gods by participation in grace; Psalm 81:6: "I have said: you are gods"; 2 Peter 1:4: "through whom he has given us great and precious promises, that by these we may be made partakers of the divine nature." Likewise, that they should be taken up into a unity of affection: because "he who adheres to God is one spirit," 1 Corinthians 6:17. Romans 8:29: "whom he foreknew, to be made conformable to the image of his Son, that he might be the firstborn among many brethren." Thus, therefore, God the Father has set a greater good for the Son according to both natures than the Son has for the disciples, yet a similar one, as has been said. "Abide in my love" — as if he were saying: since you have received so great a benefit from my love, abide in it, namely, that you may love me; or, "abide in my love," because I love you, namely, abide in my grace, that you may not fall away from the goods which I have prepared for you. And this exposition fits better, so that the sense is: that you persevere in this state, namely, that you be loved by me through the effect of grace; 1 Corinthians 7:20: "let every man abide in the calling in which he was called"; 1 John 4:16: "he who abides in charity, abides in God, and God in him." Here he shows what it is to abide in his love, and first he shows that this is to keep his commandment; second he makes it clear by an example, at the place, "as I also have kept my Father's commandments"; third he excludes a doubt, at the place, "these things I have spoken to you, that my joy may be in you." He says therefore, "abide in my love," and this you will do if you keep my commandments: for thus you will abide in my love. For the observance of the commandments is an effect of divine love, not only of that love by which we love, but of that by which he himself loves us. For from the fact that he himself loves us, he moves us and helps us to fulfill his commandments, which cannot be fulfilled except through grace, 1 John 4:10: "in this is charity: not as though we had loved God, but because he first loved us." He then adds an example for this, saying, "as I also have kept my Father's commandments." For just as the love with which the Father loves him is an example of the love with which he himself loves us, so he willed that his own obedience should be an example of our obedience. For Christ, by this, showed that he abode in the love of the Father, because in all things he kept his commandments. For he even endured death, Philippians 2:8: "he became obedient to the Father unto death, even the death of the cross." He abstained from every sin; 1 Peter 2:22: "who did no sin, neither was guile found in his mouth." These things are to be understood of Christ according as he is man; above, John 8:29: "he has not left me alone, because I always do the things that please him." And therefore he says: I abide in his love, because nothing in me, according as I am man, is contrary to his love. Lest they believe that he admonishes them to keep his commandments for his own advantage, and not that of the disciples, he says, "these things I have spoken to you" — namely, that you may keep my commandments for your own good, namely, that my joy may be in you. For love is the cause of joy: for each one rejoices over the thing loved. Now God loves both himself and the creature, especially the rational creature, to whom he communicates an infinite good. Christ therefore rejoices from eternity over two things: namely, over his own good and that of the Father; Proverbs 8:30: "I was delighted before him, playing in the world." Likewise, over the good of the rational creature; the same, Proverbs 8:31: "my delights are to be with the children of men" — that is, in this, that I am communicated to the children of men; and over these things he rejoices from eternity; Isaiah 62:5: "your God shall rejoice over you." The Lord therefore wills that, through the observance of his commandments, we be made partakers of his joy; hence he says, "that my joy" — namely, that with which I rejoice over my divinity and that of the Father — "may be in you": which is nothing other than eternal life, which is joy concerning the truth, as Augustine says; as if he were saying: that you may have eternal life; Job 22:26: "then you shall abound with delights over the Almighty." "And your joy" — that is, the joy with which I rejoice over my humanity — "may be filled." For the goods over which we rejoice are either imperfect, or are had imperfectly; and therefore joy in this life cannot be full. But it will be full when we attain perfect goods perfectly; Matthew 25:21: "enter into the joy of your lord." Here the Lord shows what his commandments are, and first he sets forth what his commandment is; second he brings in an example, at the place, "as I have loved you"; third he recalls a benefit, at the place, "you are my friends." Now the commandment which he sets down is the commandment of charity, which he wills to be kept. "This is," he says, "my commandment, that you love one another." But since there are many other commandments of the Lord in sacred discourse, it is asked why he says that the observance of charity alone is his commandment. To which, according to Gregory, it must be said that charity is the root and the end of all the virtues. Root indeed, because from charity confirmed in the heart of man, man is moved to fulfill all the other commandments; Romans 13:8: "he who loves his neighbor has fulfilled the law." Therefore all the commandments are ordered, as it were, to this — that man should do good to his neighbor, and not trouble him — which indeed is done chiefly out of charity. It is also the end, because all the commandments are ordered to it, and are made firm in charity alone; 1 Timothy 1:5: "the end of the commandment is charity." He says therefore, "this is my commandment, that you love one another," as if to say that from charity all things proceed as from a principle, and in charity all things are ordered as to an end. For, as Gregory says, just as many branches of a tree come forth from one root, so many virtues are generated from one root: nor does the branch of a good work have any greenness, if it does not abide in the root of charity. But since it is said in Matthew 22:40 that on the love not only of God, but also of neighbor, the law and the prophets depend, why does he here make mention only of the love of neighbor? But it must be said that the one is included in the other: for he who loves God must of necessity love his neighbor and the things that are God's; and he who loves his neighbor for God's sake must of necessity love God — for although the objects are diverse, yet the acts themselves, by consequence, are one. There is, however, a twofold reason why he makes mention rather of the love of neighbor than of God. One, namely, because in this he intends to instruct them, and to lead them as to how they should edify their neighbors, and how they might become strong to bear the tribulations of persecutors; and for both of these the charity of neighbor is necessary. Here he makes clear, by an example, how we ought to love our neighbor — namely, in the way that Christ loved us. Now Christ loved us in an ordered way and effectively. In an ordered way, indeed, because he loved nothing in us except God, and in order to him; Ecclesiasticus 24:24: "I am the mother of fair love," etc. Effectively, however, because he loved to such an extent that he handed himself over for us; Ephesians 5:2: "he loved us, and delivered himself up for us, an offering and a sacrifice to God for an odor of sweetness." We ought therefore to love our neighbors, namely, holily unto good, and effectively, namely, so that we show our love by deed; 1 John 3:18: "let us not love in word, nor in tongue, but in deed and in truth." "Greater love than this no man has, than that a man lay down his life for his friends." Here he shows the effectiveness of love, which is that one should endure death for his friends, which is a sign of the greatest love. But against this it is objected, that a sign of greater love is said to be when someone lays down his life for his enemies, as Christ did; Romans 5:8: "God commends his charity toward us: because when as yet we were sinners, according to the appointed time, Christ died for us." To which it must be said that Christ did not lay down his life for us as enemies, in the sense that we should remain enemies, but that he might make us friends: or, although they were not friends as loving, they were nevertheless friends as being loved. It is, however, manifest that it is a sign of the greatest love to lay down one's life for one's friends, because, in the order of things to be loved, four are ordered: namely, God, our own soul, our neighbor, and our body. And we ought to love God above ourselves and above our neighbors, so that for God we ought to give up ourselves — namely soul and body — and our neighbor. But for our own soul we ought to lay down the body, yet not to give up the soul itself. But for our neighbor we ought to expose our bodily life and body for the neighbor's salvation: and therefore, since bodily life is the chief thing that we have after the soul, it is therefore the chief thing to expose it for our neighbor, and it is a sign of greater love; 1 John 4:9: "in this the charity of God appeared in us, because God sent his only-begotten Son into the world, that we may live by him."”

“Greater love hath no man than this,.... By these words our Lord shows, how far love to another should extend, even to the laying down of our lives for the brethren; which is the highest instance of love among men; that a man lay down his life for his friends; and in which believers, should not come short of them; and also his great love to his people, and explains what he had just said, "as I have loved you", Joh 13:34; which in a little time would be seen, by his laying down his life for them: for he not only came down from heaven, and laid aside his glory and royal majesty, but he laid down his life; not his gold and silver, and the riches of this world, which were all his, but his life; than which, nothing is dearer to a man, is himself, his all: and besides, Christ's life was not a common one, it was not the life of an innocent person only, or the life of a mere man, but of a man in union with the Son of God; it was the Lord of glory and Prince of life, who was crucified, and slain; a life that was entirely at his own dispose; it had never been forfeited by sin, nor could it have been forced away from him by men or devils; it was laid down of and by himself, freely and voluntarily; and that "for", in the room, and instead of his people, as a ransom for them; he being their surety and substitute, and standing in their legal place and stead, he took their sins upon him, bore the curse of the law, sustained his Father's wrath, and all the punishment due to sin; and so suffered death, the death of the cross; the just, in the room and stead of the unjust; the persons for whom be laid down his life, are described as "his friends"; not that they were originally so; being enemies and enmity itself to God, when he laid down his life for them, and reconciled them; they were not such as had carried themselves friendly, or had shown any love and affection to him, but all the reverse: but they are so called, because he had chosen them for his friends; he had pitched upon them, and resolved to make them so; and by dying for them, reconciled them who were enemies; and in consequence of this, by his Spirit and grace, of enemies makes them friends; so that his love in dying for his people, is greater than any instance of love among men: he laid down his life for his enemies, without any sinister selfish views, and that freely and voluntarily; whereas among men, when one man has laid down his life for others, either they have been very deserving, or he has been forced to it, or it has been done with the view of popular applause and vain glory.”

“That ye love one another - See on Joh 13:34 (note). So deeply was thus commandment engraved on the heart of this evangelist that St. Jerome says, lib. iii. c. 6, Com. ad Galat., that in his extreme old age, when he used to be carried to the public assemblies of the believers, his constant saying was, Little children, love one another. His disciples, wearied at last with the constant repetition of the same words, asked him, Why he constantly said the same thing? "Because (said he) it is the commandment of the Lord, and the observation of it alone is sufficient." Quia praeceptum Domini est, et, si solum fiat, sufficit.”