6 But this, as we have said, brethren, is perfect charity. He that is born of God has it. Mark, my beloved, see what I say. Behold, a man has received the Sacrament of that birth, being baptized; he has the Sacrament, and a great Sacrament, divine, holy, ineffable. Consider what a Sacrament! To make him a new man by remission of all sins! Nevertheless, let him look well to the heart, whether that be thoroughly done there, which is done in the body; let him see whether he have charity, and then say, I am born of God. If however he have it not, he has indeed the soldier's mark upon him, but he roams as a deserter. Let him have charity; otherwise let him not say that he is born of God. But he says, I have the Sacrament. Hear the Apostle: “If I know all mysteries, and have all faith, so that I can remove mountains, and have not charity, I am nothing.”
Source: Homilies on the First Epistle of John (New Advent)