By Robert Roberts
Paul commands withdrawal from every brother obeying not the word he wrote, by 2 Thess. His word in that epistle includes an exhortation to the Thessalonians (and therefore to ALL believers to all time, until the Lord change it) that they "stand fast and hold to the traditions (teachings) which they had been taught, WHETHER BY WORD OR BY PAUL'S EPISTLE (2:15).
Hence the duty of withdrawal applies to EVERY CASE involving the deliberate and unrepentant disobedience of ANY of the apostolic precepts.
--1872