From a treatise on John by Saint Augustine

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…