Charles Ellicott Commentary 2 Thessalonians 3:15

"And [yet] count him not as an enemy, but admonish him as a brother." — 2 Thessalonians 3:15 (ASV)

Yet—The original is simply And, which is much more beautiful, implying that this very withdrawal from brotherly fellowship was an act of brotherly kindness.

An enemy—In the private, not the public, sense. “Do not think of him as one with whom you must be in a feud, to be thwarted and humbled on every occasion.” St. Chrysostom exclaims, “How soon the father’s heart breaks down!”

Admonish him as a brother—How was this to be done without associating with him? Perhaps the presbyters, to whom the work of “admonishing,” or “warning,” specifically belonged (see 1 Thessalonians 5:12; 1 Thessalonians 5:14), were to visit them in private for that purpose. Or possibly, the admonition was to consist in the act of separation itself, and not in verbal reproof at all.