1 Thessalonians 4:9

It is through grace that we not only discover what ought to be done but also that we do what we have discovered. That is, not only that we believe what ought to be loved but also that we love what we have believed. If this grace is to be called "teaching," let it at any rate be called "teaching" in such a manner that God may be believed to infuse it, along with an ineffable sweetness, more deeply and more internally. This teaching, therefore, would be not only by their agency who plant and water from without but likewise by God also who ministers in secret his own increase. All this is in such a way that God not only exhibits truth but likewise imparts love.… Thus the apostle speaks to the Thessalonians, "As touching love of the brothers, you have no need that I write to you, for you yourselves have been taught by God to love one another."

The blessed apostle, like a true and spiritual physician, either seeing this disease which springs from the spirit of lethargy already creeping in, or foreseeing through the Holy Spirit that it would arise among monks, is quick to anticipate it by the healing medicines of his directions. For when he writes to the Thessalonians, he first sounds like a skillful and excellent physician, applying the soothing and gentle remedy of his words to the sickness of his patients. He begins with charity … that this deadly wound, having been treated with a milder remedy, might cease its angry festering and more easily bear severer treatment. He writes, "But concerning brotherly charity you have no need that I write to you, for you yourselves are taught of God to love one another. For this you do toward all the brothers in the whole of Macedonia." He first began with the soothing application of praise and made their ears submissive and ready for the remedy of the healing words.… At last with difficulty he breaks out into that at which he was driving before. He gave the first aim. "Take pains to be quiet." Then Paul adds a second: "Mind your own business." And a third as well: "Work with your own hands, as we commanded you." … [The upshot is] that one who does not dutifully and peacefully work for his daily food with his own hands is sure to view enviously another's gifts and blessings. You see what conditions, serious and shameful, may spring solely from the malady of leisure.

"But concerning love of the brethren we have no need to write unto you: for ye yourselves are taught of God to love one another; for indeed ye do it toward all the brethren, and those which are in all Macedonia." Why then having discoursed with them earnestly concerning chastity, and being about to discourse about the duty of working, and about the not sorrowing for the departed, does he introduce that which was the principal of all good things, love, as if he were passing it over, saying, "We have no need to write to you"? This also is from his great wisdom, and belongs to spiritual instruction. For here he shows two things. First, that the thing is so necessary, as not to require instruction. For things that are very important are manifest to all. And secondly, by saying this he makes them more ashamed than if he had admonished them. For he who thinks that they have behaved aright, and therefore does not admonish them, even if they had not behaved aright, would the sooner lead them to it. And observe, he does not speak of love towards all, but of that towards the brethren. "We have no need to write unto you." He ought then to have been silent, and to say nothing, if there was no need. But now by saying there is no need, he has done a greater thing, than if he had said it. "For ye yourselves are taught of God." And see with how high a praise he has made God their Teacher in this matter. Ye need not, he says, to learn from man. Which also the prophet says, "and they shall all be taught of God." (Isa. liv. 13) "For ye yourselves," he says, "are taught of God to love one another. For indeed ye do it toward all the brethren, and those which are in all Macedonia"; and toward all the others, he means. These words are very encouraging to make them do so. And I do not merely say, that ye are taught of God, but I know it from the things which you do. […]

Salvation, accordingly, is the following of Christ: "For that which is in Him is life." "Verily, verily, I say unto you, He that heareth My words, and believeth on Him that sent Me, hath eternal life, and cometh not into condemnation, but hath passed from death to life." Thus believing alone, and regeneration, is perfection in life; for God is never weak.

Then when Paul remarks: But concerning love of the brethren you have no need to have any one write to you, he discourages them from remaining idle. It should be realized, as Jerome says in the letter to the Galatians, that the Thessalonians were generous, …