John Chrysostom

"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"? …

Homily on 1 Thessalonians 6 ↗

Theophylact of Ohrid

The Apostle no longer speaks of love toward all, but of love toward the brethren. By the very omission he already exhorts, achieving two purposes: first, this matter is so necessary that there is no need even to learn it, for everyone knows that it holds particular importance for all. Second, by this he admonishes them all the more, urging them not to fall below the opinion he had of them, considering them already corrected. See how he praises them, saying that God Himself teaches them this virtue. …

Commentary on 1 Thessalonians ↗

Clement of Alexandria

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. For as His will is work, and this is named the world; so also His counsel is the salvation of men, and this has been called the church. …

The Instructor Book 1 ↗

Augustine of Hippo

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. …

On the Grace of Christ 12.13-13.14

Thomas Aquinas

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, and that it was the custom among the rich to give away a great deal; as a result the poor idly depended on their benefits without looking for work, but rather wasted time in their homes. …

Commentary on 1 Thessalonians ↗