“This is the love of God, that we keep his commandments” (1 Jn 4:3). You have already heard this: “On these two commandments hang all the law and the prophets.” See how Christ did not want to divide you over lots of pages! “On these two commandments hang all the law and the prophets.” On which two commandments? “You shall love the Lord your God with all your heart and with all your soul and with all your mind,” and, “You shall love your neighbor as yourself” (Mt22:37-40) These are the two commandments that this whole Epistle is talking about. If you hold fast to love, then, you’ll be safe. Why fear that you will do someone evil? Who acts evilly toward someone he loves? Love, and you can only do good….
It’s not our task to enlarge your hearts; ask God for the gift of loving one another. Love all men, even your enemies, not because they are your brothers but so that they may become your brothers, so that you may always be on fire with fraternal love whether to one who has become your brother or toward an enemy that he may become your brother by being loved. Whenever you love a brother you are loving a friend. He is now with you, he is now linked with you in catholic unity. If you live well, you love the one who, once an enemy, has become your brother. … All our love is a brotherly love toward Christians, toward all Christ’s members. The discipline of charity, brothers and sisters, its strength, its flower, its fruit, its beauty, its pleasantness, its food, its drink, its embraces, know no satiety. If love so delights us as we wander, imagine how we shall rejoice in our homeland! (Augustine on I John, Hom 10, 7; PL 35, 2059)