Jn.: 13:31-35: Homily of Saint Augustine (Sermon 350, 1)
“My brothers, he whose heart is filled with charity, understands without error and observes without toil, the varied abundant and vast doctrine of the Sacred Scriptures, as the Apostle says: The fullness of the law is charity (Rom. 13:10), and in another place, he says: The end of the law is charity coming from a pure heart, good conscience and sincere faith. (1 Tim. 1:5) What is then the end of the law, if not the fulfillment of the law? And what is then the fulfillment of the law, if not the fullness of the law? Then, what he said here, The fullness of the law is charity, is the same thing that he said in another: The end of the law is charity.
It cannot be doubted in any way that man is the temple of God, in whom charity dwells. In fact, John also says: God is love. The Apostles, while they are telling us this and commending to us the primacy of charity, are signifying that they could have belched forth only that which they had eaten. The Lord Himself, who nourished them with the word of truth and charity, He who is the living bread who came down from heaven, said: I shall give you a new commandment, that you love one another. (Jn. 13:34) In addition, he affirmed: In this, they will all know that you are my disciples, if you shall have loved one another. (Jn. 13: 35)
In fact, He who came to give death to the corruption of the flesh through the ignominy of the cross and to unfasten the old chain of our death with the newness of his death, made man new with the new commandment. That man might die was of old. So that this reality might not happen in man, a new reality happened: that God should die. But since He died in the flesh, and not in divinity, He did not allow the flesh to be eternally destroyed through the everlasting life of His divinity.”
(Trans. By Fr. Romeo Potencio,OAR)