Love works no ill to his neighbor: therefore love is the fulfilling of the law.
Read Chapter 13
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. Commentary on Paul’s Epistles.
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.
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: "