Augustine of Hippo
Catena Aurea · Johannesevangelium 15
This is my commandment, That ye love one another, as I have loved you. Greater love hath no man than this, that a man lay down his life for his friends. Ye are my friends, if ye do whatsoever I command you. Henceforth I call you not servants; for the servant knoweth not what his Lord doeth: but I have called you friends; for all things that I have heard of my Father I have made known unto you. Ye have not chosen me, but I have chosen you, and ordained you, that ye should go and bring forth fruit, and that your fruit should remain: that whatsoever ye shall ask of the Father in my name, he may give it you.
(viii. de Trin. c. viii) From one and the same love, we love God and our neighbour; but God for His own sake, our neighbour for God’s. So that, there being two precepts of love, on which hang all the Law and the Prophets, to love God, and to love our neighbour, Scripture often unites them into one precept. For if a man love God, it follows that he does what God commands, and if so, that he loves his neighbour, God having commanded this. Wherefore He proceeds: Ye are My friends, if ye do whatsoever I command you.