From a treatise on John by Saint Augustine, bishop
The new commandment
A new commandment I give you, that you love one another. This commandment that he is giving them is a new one, the Lord Jesus tells his disciples. Yet was it not contained in the Old Law, where it is written: You shall love your neighbor as yourself? Why does the Lord call it new when it is clearly so old? Or is the commandment new because it divests us of our former selves and clothes us with the new man? Love does indeed renew the man who hears, or rather obeys its command; but only that love which Jesus distinguished from a natural love by the qualification: As I have loved you.
This is the kind of love that renews us. When we love as he loved us we become new men, heirs of the new covenant and singers of the new song. My brothers, this was the love that even in bygone days renewed the holy men, the patriarchs and prophets of old. In later times it renewed the blessed apostles, and now it is the turn of the Gentiles. From the entire human race throughout the world this love gathers together into one body a new people, to be the bride of God’s only Son. She is the bride of whom it is asked in the Song of Songs: Who is this who comes clothed in white? White indeed are her garments, for she has been made new; and the source of her renewal is none other than this new commandment.
And so all her members make each other’s welfare their common care. When one member suffers, all the members suffer with him, and if one member is glorified all the rest rejoice. They hear and obey the Lord’s words: A new commandment I give you, that you love one another; not as men love one another for their own selfish ends, nor merely on account of their common humanity, but because they are all gods and sons of the Most High. They love one another as God loves them so that they may be brothers of his only Son. He will lead them to the goal that alone will satisfy them, where all their desires will be fulfilled. For when God is all in all, there will be nothing left to desire.
This love is the gift of the Lord who said: As I have loved you, you also must love one another. His object in loving us, then, was to enable us to love each other. By loving us himself, our mighty head has linked us all together as members of his own body, bound to one another by the tender bond of love.