34 A new commandment I give unto you, That ye love one another; as I have loved you, that ye also love one another.
[AD 108] Ignatius of Antioch on John 13:34
Let no man's place, or dignity, or riches, puff him up; and let no man's low condition or poverty abase him. For the chief points are faith towards God, hope towards Christ, the enjoyment of those good things for which we look, and love towards God and our neighbour. For, "Thou shall love the Lord thy God with all thy heart, and thy neighbour as thyself." And the Lord says, "This is life eternal, to know the only true God, and Jesus Christ whom He has sent." And again, "A new commandment give I unto you, that ye love one another. On these two commandments hang all the law and the prophets." Do ye, therefore, notice those who preach other doctrines, how they affirm that the Father of Christ cannot be known, and how they exhibit enmity and deceit in their dealings with one another. They have no regard for love; they despise the good things we expect hereafter; they regard present things as if they were durable; they ridicule him that is in affliction; they laugh at him that is in bonds.

[AD 380] Apostolic Constitutions on John 13:34
He who then had forbidden murder now forbids anger without cause. He who had forbidden adultery now forbids all unlawful lust. He who had forbidden stealing now pronounces him most happy who supplies those that are in want out of his own labors. He who had forbidden hatred now pronounces him blessed who loves his enemies.

[AD 407] John Chrysostom on John 13:34
(Hom. lxxii. 3) Or, as I have loved you: for My love has not been the payment of something owing to you, but had its beginning on My side. And ye ought in like manner to do one another good, though ye may not owe it.

[AD 430] Augustine of Hippo on John 13:34
The Lord Jesus declares that He is giving His disciples a new commandment, that they should love one another. "A new commandment," He says, "I give unto you, that ye love one another." But was not this already commanded in the ancient law of God, where it is written, "Thou shalt love thy neighbor as thyself"? Why, then, is it called a new one by the Lord, when it is proved to be so old? Is it on this account a new commandment, because He hath divested us of the old, and clothed us with the new man? For it is not indeed every kind of love that renews him that listens to it, or rather yields it obedience, but that love regarding which the Lord, in order to distinguish it from all carnal affection, added, "as I have loved you." For husbands and wives love one another, and parents and children, and all other human relationships that bind men together: to say nothing of the blame-worthy and damnable love which is mutually felt by adulterers and adulteresses, by fornicators and prostitutes, and all others who are knit together by no human relationship, but by the mischievous depravity of human life. Christ, therefore, hath given us a new commandment, that we should love one another, as He also hath loved us. This is the love that renews us, making us new men, heirs of the New Testament, singers of the new song. It was this love, brethren beloved, that renewed also those of olden time, who were then the righteous, the patriarchs and prophets, as it did afterwards the blessed apostles: it is it, too, that is now renewing the nations, and from among the universal race of man, which overspreads the whole world, is making and gathering together a new people, the body of the newly-married spouse of the only-begotten Son of God, of whom it is said in the Song of Songs, "Who is she that ascendeth, made white?" Made white indeed, because renewed; and how, but by the new commandment! Because of this, the members thereof have a mutual interest in one another; and if one member suffer, all the members suffer with it; and one member be honored, all the members rejoice with it. For this they hear and observe, "A new commandment I give unto you, that ye love one another:" not as those love one another who are corrupters, nor as men love one another in a human way; but they love one another as those who are God's, and all of them sons of the Highest, and brethren, therefore, of His only Son, with that mutual love wherewith He loved them, when about to lead them on to the goal where all sufficiency should be theirs, and where their every desire should be satisfied with good things. For then there will be nothing wanting they can desire, when God will be all in all. An end like that has no end. No one dieth there, where no one arriveth save he that dieth to this world, not that universal kind of death whereby the body is bereft of the soul; but the death of the elect, through which, even while still remaining in this mortal flesh, the heart is set on the things which are above. Of such a death it is that the apostle said, "For ye are dead, and your life is hid with Christ in God." And perhaps to this, also, do the words refer,"Love is strong as death." For by this love it is brought about, that, while still held in the present corruptible body, we die to this world, and our life is hid with Christ in God; yea, that love itself is our death to the world, and our life with God. For if that is death when the soul quits the body, how can it be other than death when our love quits the world? Such love, therefore, is strong as death. And what is stronger than that which conquers the world?

Think not then, my brethren, that when the Lord says, "A new commandment I give unto you, that ye love one another," there is any overlooking of that greater commandment, which requires us to love the Lord our God with all our heart, and with all our soul, and with all our mind; for along with this seeming oversight, the words "that ye love one another" appear also as if they had no reference to that second commandment, which says, "Thou shalt love thy neighbor as thyself." For "on these two commandments," He says, "hang all the law and the prophets." But both commandments may be found in each of these by those who have good understanding. For, on the one hand, he that loveth God cannot despise His commandment to love his neighbor; and on the other, he who in a holy and spiritual way loveth his neighbor, what doth he love in him but God? That is the love, distinguished from all mundane love, which the Lord specially characterized, when He added, "as I have loved you." For what was it but God that He loved in us? Not because we had Him, but in order that we might have Him; and that He may lead us on, as I said a little ago, where God is all in all. It is in this way, also, that the physician is properly said to love the sick; and what is it he loves in them but their health, which at all events he desires to recall; not their sickness, which he comes to remove? Let us, then, also so love one another, that, as far as possible, we may by the solicitude of our love be winning one another to have God within us. And this love is bestowed on us by Him who said, "As I have loved you, that ye also love one another." For this very end, therefore, did He love us, that we also should love one another; bestowing this on us by His own love to us, that we should be bound to one another in mutual love, and, united together as members by so pleasant a bond, should be the body of so mighty a Head.

[AD 430] Augustine of Hippo on John 13:34
(Tr. lxv. 1) And now He teaches them how to fit themselves to follow Him: A new commandment I give unto you, that ye love one another. (Levit. 19:18) But does not the old law say, Thou shall love thy neighbour as thyself? Why then does He call it a new commandment? Is it because it strips us of the old man, and puts on us the new? That it renews the hearer, or rather the doer of it? Love does do this; but it is that love which our Lord distinguishes from the carnal affection: As I have loved you, that ye also love one another. Not the love with which men love one another, but that of the children of the Most High God, who would be brethren of His only-begotten Son, and therefore love one another with that love with which He loved them, and would lead them to the fulfilment of their desires.

(Tr. lxiv. 2) But do not think that that greater commandment, viz. that we should love the Lord our God, is passed by. For, if we understand the two precepts aright, each is implied in the other. He who loves God cannot despise His commandment that he should love his neighbour; and he who loves his neighbour in a heavenly spiritual way, in the neighbour loves God. That is the love which our Lord distinguishes from all human love, when He adds, As I have loved you. For what did He, in loving us, love, but God in us; not who was in us, but so that He might be? Wherefore let each of us so love the other, as that by this working of love, we make each other the habitations of God.

[AD 444] Cyril of Alexandria on John 13:34
Well and truly writes the inspired Paul: Wherefore if any man is in Christ, he is a new creature: the old things are passed away; behold all things are become new. For Christ does renew us, and fashions us again to a newness of life which is unknown to and untravelled by the rest of mankind, who love to regulate their lives by the Law, and remain constant to the precepts given by Moses. For the Law makes nothing perfect, as it is written; but it is very evident that the standard of reverence towards God involved in the commands of our Saviour is the highest possible. For this is why He Himself somewhere says to us: Verily, verily, I say unto you, Except your righteousness shall exceed the righteousness of the scribes and Pharisees, ye shall in no wise enter into the kingdom of heaven. We do not wish to struggle against the manner of life of the Jews, and yet except we outstrip very decisively the righteousness contained in the Law, I doubt if we should ever enter into the kingdom of heaven. And we do not mean to assert that the Law as given by Moses was useless and unprofitable: for it has brought to us, albeit imperfectly, a knowledge of good, or at any rate has been found to be a tutor for our instruction as to the nature of the Gospel dispensation. And in bringing before us by hints and types a pattern of the true worship, it imprinted on our minds the dim outline of the teaching we learn from Christ. Hence, surely Christ Himself also said: For I say unto you, that every scribe who hath been made a disciple to the kingdom of heaven is like unto a rich man, which bringeth forth out of his treasure things new and old. For in very truth it is the highest form of spiritual wealth, that a man should be well versed in the words spoken by Moses, and have all the good that can be derived from them treasured up in his mind, and besides should have added to this store the beauty of the evangelic teaching, and so have twofold ground for boasting, in his knowledge as well of the ancient as of the new laws. Therefore our Lord Jesus the Christ, by way of showing that His commandment was better than the ancient one, and that His preaching of salvation was as yet foreign to those who regulated their lives by the Law, now that He is about to ascend into heaven, lays down the law of love as a foundation and corner-stone of all that is good, meaning by love not that which was in accordance with, but that which transcended, the Mosaic Law. Therefore He says: A new commandment I give unto you, that ye love one another. "But tell me now,' some one may say, "why He has called this commandment new, when He had said to former generations by the voice of Moses: Thou shalt love the Lord thy God with all thy heart and with all thy mind, and thy neighbour as thyself. For see, while setting love to God in its fitting place, in the forefront of and in preeminence to all other affections, He has there introduced in the very next place our mutual love, and has joined with our love to God love to each other, implying that in no other way would love to God rightly exist, except it were accompanied by the love which is due to our neighbour. For we all are brethren one of another. For instance, the very wise John, most excellent alike in knowledge and in teaching, says: He that loveth his brother loveth God. How then cometh a new commandment by Christ, although the very same had been declared by the ancient laws?" But notice, I pray you, the justifying clause; look at the illustration used. He does more than say: A new commandment give I unto you, that ye love one another; He plainly signifies the novelty involved in His command, and the extent by which the love that He enjoins surpasses that old idea of mutual love, by straightway adding the words: Even as I have loved you, that ye also love one another.

We must investigate therefore the question how the Christ loved us, in order to understand clearly the full force of the words used. For then we shall indeed perceive, and that very easily, the novel character and the changed nature of the commandment now given. We know that, being in the form of God, He counted it not a prize to be on an equality with God, but emptied Himself, taking the form of a servant, being made in the likeness of men; and being found in fashion as a man, He humbled Himself, becoming obedient even unto death, yea, the death of the cross. And again: though He was rich, yet He became poor, as Paul elsewhere testifies to us. Dost thou see the novelty of His love towards us? For whereas the Law enjoined the necessity of loving our brethren as ourselves, our Lord Jesus the Christ on the other hand loved us far more than He loved Himself, Else He would never have descended to our humiliation from His original exaltation in the form of God and on an equality with God the Father, nor would He have undergone for our sakes the exceeding bitterness of His death in the flesh, nor have submitted to buffetings from the Jews, to shame, to derision, and all His other sufferings: speaking briefly, so as not to protract our argument to endless length by enumerating everything in detail. Nay, He would never have become poor from being rich, if He had not loved us very exceedingly more than Himself. Marvellous then indeed was the extent of His love. So also He would have us be minded, keeping ever our love to our brethren as superior to all other motives, such as reputation or riches; not hesitating to descend if need be even to death in the flesh, so that we may secure the salvation of our neighbour. And this is exactly what the blessed disciples of our Saviour have done, as also have those that followed in their train; reckoning the salvation of others superior to their own life, enduring toil of all kinds, and suffering the extremest of evils, that so they might sa\e the souls of those that were perishing. For instance, Paul in one place saith: I die daily; and in another again: Who is weak, and I am not weak? Who is made to stumble, and I burn not? Thus the Saviour urges us to practise ever the love that transcends the Law as the root of all true and perfect devotion to God; well knowing that so, assuredly, and not otherwise, we shall be most highly approved in the sight of God, and by tracing out the Divine beauty of the love by Him implanted in us we shall attain to the enjoyment of great and perfect blessings.

[AD 444] Cyril of Alexandria on John 13:34
He plainly indicates the novelty involved in his command here—and the extent to which the love he enjoins here surpasses the old idea of mutual love—by adding the words “Even as I have loved you, you also should love one another.” … The law of Moses mandated the necessity of loving our brothers as ourselves, yet our Lord Jesus the Christ loved us far more than he loved himself. Otherwise, he would have never descended to our humiliation from his original exaltation in the form of God and on an equality with God the Father, nor would he have undergone for our sakes the exceptional bitterness of his death in the flesh, nor have submitted to beatings from the Jews, to shame, to derision, and all his other sufferings too numerous to mention. Being rich, he would never have become poor if he had not loved us far more than he loved himself. It was indeed something new for love to go as far as that! Christ commands us to love as he did, putting neither reputation, wealth or anything else before love of our brothers and sisters. If need be, we even need to be prepared to face death for our neighbor’s salvation as our Savior’s blessed disciples did, as well as those who followed in their footsteps. To them the salvation of others mattered more than their own lives, and they were ready to do anything or to suffer anything to save souls that were perishing.