Augustine of Hippo — as excerpted in the Catena Aurea on John 13:33-35

“(Tr. lxiv. 2) But do not think that that greater commandment, viz. that we should love the Lord our God, is passed by. For, if we understand the two precepts aright, each is implied in the other. He who loves God cannot despise His commandment that he should love his neighbour; and he who loves his neighbour in a heavenly spiritual way, in the neighbour loves God. That is the love which our Lord distinguishes from all human love, when He adds, As I have loved you. For what did He, in loving us, love, but God in us; not who was in us, but so that He might be? Wherefore let each of us so love the other, as that by this working of love, we make each other the habitations of God.”