John Chrysostom

"But ye, brethren, be not weary in well doing." See how immediately the fatherly heart was overcome. He was not able to carry out his reproof farther, but again pitied them. And see with what discretion! He has not said, But pardon them, until they are amended; but what? "But ye, be not weary in well doing." Withdraw yourselves, he says, from them, and reprove them; do not, however, suffer them to perish. …

Homily on 2 Thessalonians 5 ↗

Theophylact of Ohrid

See how quickly the fatherly heart was softened — he immediately took pity on them. Withdraw from them, he says, and separate yourselves, but nevertheless do not allow them to starve to death. So then, what will come of this? Surely no one, being confident that I will feed him, will remain idle? It is enough for you to withdraw from him and not embolden him, acting as though you are angry with him. Even if someone after all this does not reform, still do not grow weary of doing good.

Commentary on 2 Thessalonians ↗

Thomas Aquinas

Then when he says "but you, brethren," he applies two remedies on the side of the others who are not sinning. First, that they should not cease doing good; second, that they correct them, at "and if any man." He says, therefore, "but you, brethren, do not be weary in doing good," as though to say: do not grow weary in doing good, even though the idle are abusing it. "Doing good, we do not grow weary" (Gal 6:9). …

Commentary on 2 Thessalonians ↗