Augustine of Hippo — as excerpted in the Catena Aurea on John 15:17-21

“(Tract. lxxxvii. 1) Our Lord had said, I have ordained that ye should walk, and bring forth fruit. Love is this fruit. Wherefore He proceeds: These things I command you, that ye love one another. (Gal. 5:22) Hence the Apostle saith: The fruit of the Spirit is love; and enumerates all other graces as springing from this source. Well then doth our Lord commend love, as if it were the only thing commanded: seeing that without it nothing can profit, with it nothing be wanting, whereby a man is made good.”