But, behold, now, if I shall ask any one of you whether he loveth God, he will answer with all boldness and quietness of spirit "I do love him." But at the very beginning of this day's Lesson from the Gospel, ye have heard what the Truth saith " If a man love Me, he will keep My word." The test, then, of love, is whether it is showed by works. Hence the same John hath said in his Epistle I. iv. 20, v. 3 "If a man say, I love God, and keepeth not His commandments, He is a liar." Then do we indeed love God, and keep His commandments, if we deny ourselves the gratification of our appetites. Whosoever still wandereth after unlawful desires, such an one plainly loveth not God, for he saith, Nay, to that which God willeth.
Lesson ii, Roman Breviary, Homily of St. Gregory, Pope
Homily 30 on the Gospels