4 And by what do we know that we love the sons of God? By this, “that we love God, and do His commandments.” We sigh here, by reason of the hardness of doing the commandments of God. Hear what follows. O man, at what do you toil in loving? In loving avarice. With toil is that loved which you love: there is no toil in loving God. Avarice will enjoin you labors, perils, sore hardships and tribulations; and you will do its bidding. To what end? That you may have that with which you shall fill your chest, and lose your peace of mind.
You felt yourself haply more secure before you had it, than since you began to have. See what avarice has enjoined you. You have filled your house, and art in dread of robbers; hast gotten gold, lost your sleep. See what avarice has enjoined you. Do, and you did. What does God enjoin you! Love me. You love gold, you will seek gold, and perchance not find it: whoever seeks me, I am with him. You will love honor, and perchance not attain unto it: who ever loved me, and did not attain?
God says to you, you would make you a patron, or a powerful friend: you seek a way to his favor by means of another inferior. Love me, says God to you: favor with me is not had by making interest with some other: your love itself makes me present to you. What sweeter than this love, brethren? It is not without reason that you heard just now in the Psalm, “The unrighteous told me of delights, but not as is Your law, O Lord.” What is the Law of God? The commandment of God. What is the commandment of God?
That “new commandment,” which is called new because it makes new: “A new commandment give I unto you, that you love one another.” Hear because this is the law of God. The apostle says, “Bear ye one another's burdens, and so shall you fulfill the law of Christ.” This, even this, is the consummation of all our works; Love. In it is the end: for this we run: to it we run; when we have come to it, we shall rest.
Source: Homilies on the First Epistle of John (New Advent)