Rom 13:10

“But that this is the first and greatest commandment, and that the next [has respect to love] towards our neighbour, the Lord has taught, when He says that the entire law and the prophets hang upon these two commandments. Moreover, He did not Himself bring down [from heaven] any other commandment greater than this one, but renewed this very same one to His disciples, when He enjoined them to love God with all their heart, and others as themselves. But if He had descended from another Father, He never would have made use of the first and greatest commandment of the law; but He would undoubtedly have endeavoured by all means to bring down a greater one than this from the perfect Father, so as not to make use of that which had been given by the God of the law. And Paul in like manner declares, "Love is the fulfilling of the law:" and [he declares] that when all other things have been destroyed, there shall remain "faith, hope, and love; but the greatest of all is love;" and that apart from the love of God, neither knowledge avails anything, nor the understanding of mysteries, nor faith, nor prophecy, but that without love all are hollow and vain; moreover, that love makes man perfect; and that he who loves God is perfect, both in this world and in that which is to come. For we do never cease from loving God; but in proportion as we continue to contemplate Him, so much the more do we love Him.”

“"God," then, being good, "is love," it is said. Whose "love worketh no ill to his neighhour," neither injuring nor revenging ever, but, in a word, doing good to all according to the image of God. "Love is," then, "the fulfilling of the law; " like as Christ, that is the presence of the Lord who loves us; and our loving teaching of, and discipline according to Christ. By love, then, the commands not to commit adultery, and not to covet one's neighbour's wife, are fulfilled, [these sins being] formerly prohibited by fear.”

“For there was no laying of accusations against each other among them, except what was friendly; neither ought there ever to be such among their followers or among believers: for the Lord says, "Do not that to another which thou wouldst not have done to thyself." And He says also, "Thou shalt love thy neighbour as thyself;" and, "Love worketh no ill to his neighbour."”

“"Love worketh no ill to his neighbor, therefore love is the fulfilling of the Law." Observe how it has both virtues, abstinence from evils (for it "worketh no ill," he says), and the working of good deeds. "For it is," he says, "the fulfilling (or filling up) of the Law;" not bringing before us instruction only on moral duties in a concise form, but making the accomplishment of them easy also. For that we should become acquainted with things profitable to us was not all that he was careful for (which is the Law's care), but also with a view to the doing of them it brought us great assistance; accomplishing not some part of the commandments, but the whole sum of virtue in us. Let us then love one another, since in this way we shall also love God, Who loveth us. For in the case of men, if you love a man's beloved, he that loveth him is contentious at it. But here He deemeth thee worthy to share His love, and hateth thee when thou sharest not. For man's love is laden with envy and grudging; but God's is free from all passion, whence also He seeketh for those to share His love. For He says, love thou with Me, and then thyself also will I love the more. You see the words of a vehement lover! If thou love My beloved, then will I also reckon Myself to be greatly beloved of thee. For He vehemently desireth our salvation, and this He showed from of old.”

“Even not to do good is wrong. For if one sees that one's neighbor is in danger of starvation, does one not kill him if, while one has an abundance, one does not give him food, though one has not used up one's own provisions? For anyone who is able to help someone close to death in whatever situation of need kills that person if he does not come to his aid.”

“The rule of love is that one should wish his friend to have all the good things he wants to have himself and should not wish the evils to befall his friend which he wishes to avoid himself. He shows this benevolence to all men. No evil must be done to any. Love of one's neighbor works no evil. Let us then love even our enemies as we are commanded, if we wish to be truly unconquered.”

“Therefore, whatever you do, do it for the love of Christ, and let the intention or end of all your actions look to him. Do nothing for the sake of human praise but everything for the love of God and the desire for eternal life. Then you will see the end of all perfection, and when you have reached it you will want nothing more.”

“He shows that love has both kinds of perfection. When he says that "love does no evil to one's neighbor," he indicates that it is abstention from evil, and with the words "love is the fulfillment of the law" he points out that it is the doing of good. Thus, love accomplishes in us the virtue indicated by the law, in all its fullness.”

“No one is saved without knowledge of himself, from which indeed the mother of salvation, humility, arises, and the fear of the Lord, which itself, just as it is the beginning of wisdom, so also is the beginning of salvation. No one, I say, is saved without that knowledge, who yet has the age and faculty of knowing. This I say on account of little children and the mentally deficient, whose case is different. What if you are ignorant of God? Can there be hope of salvation with ignorance of God? Not even this. For you can neither love one whom you do not know, nor possess one whom you have not loved. Know yourself therefore, that you may fear God; know him, that you may likewise appease him. In the one you are initiated into wisdom, in the other you are also brought to perfection, because the beginning of wisdom is the fear of the Lord, and the fullness of the law is love. Both ignorances therefore must be guarded against by you, just as without the fear and love of God salvation cannot exist. The rest are indifferent, having neither salvation if they are known, nor damnation if they are not known.”

“For sacred Scripture is principally concerned with the works of reparation. Whence it treats chiefly of faith, hope, and charity, through which virtues the soul must be reformed, and most especially of charity. Of which the Apostle says that it is the end of the commandment, insofar as it proceeds from a pure heart and a good conscience and faith unfeigned. It is the fullness of the Law, as the same Apostle says. And our Savior asserts that the whole Law and the Prophets depend on the two precepts of the same, namely the love of God and of neighbor; which two are intimated in the one Spouse of the Church, Jesus Christ, who is at once neighbor and God, at once brother and lord, at once also king and friend, at once the uncreated and incarnate Word, our maker and remaker, as the Alpha and the Omega; who is also the supreme hierarch, purging and illuminating and perfecting the spouse, namely the whole Church and every holy soul.”

“Then when he says, the love of our neighbor works no evil, he clarifies his proposition with the following syllogism: One who loves his neighbor does no evil to him. But the aim of every precept of the law is abstention from evil. Therefore, one who loves his neighbor fulfills the law. That love of neighbor does no evil is gathered from 1 Corinthians: love does not work injury (1 Cor 13:4). No matter how evil is taken here, whether for evil acts or omissions, it could refer not only to negative precepts but also to affirmative. But inasmuch as love of neighbor includes love of God, it is understood that love of neighbor excludes evil both against one's neighbor and against God. Thus, even the precepts of the first tablet are included. Finally, he draws the conclusion mainly intended, saying: therefore, love is the fulfillment of the law, i.e., the law is fulfilled and made perfect by love. My abode is in the full assembly of the saints (Sir 14:16); above all these put on love, which binds everything together in perfect harmony (Col 3:14).”

“Paul is using the words of the law to arrive at the meaning of the gospel. Therefore when he records the fulfilling of the law he ties it to the gospel, demonstrating that both have a single author. Yet in the time of Christ it was necessary to add something, viz., that we should love our enemies as well as our neighbors.… What does it mean to love an enemy, except to choose not to hate him any longer and to seek to do him no harm?… For the Lord himself on the cross prayed for his enemies in order to demonstrate what the fullness of righteousness, which he had taught, actually was.”