Passage
But if any one obey not our word by the letter, mark that man, and do not keep company with him, that he may be ashamed of himself;
But if any one obey not our word by the letter, mark that man, and do not keep company with him, that he may be ashamed of himself;
2 Thessalonians 3:12 Now such we enjoin and exhort in [the] Lord Jesus Christ, that working quietly they eat their own bread.
2 Thessalonians 3:13 But *ye*, brethren, do not faint in well-doing.
2 Thessalonians 3:14 But if any one obey not our word by the letter, mark that man, and do not keep company with him, that he may be ashamed of himself;
2 Thessalonians 3:15 and do not esteem him as an enemy, but admonish [him] as a brother.
2 Thessalonians 3:16 But the Lord of peace himself give you peace continually in every way. The Lord [be] with you all.
The verse centers on "obey", "word", "letter", "mark", "keep", "company", "ashamed", and "himself". It is saying that the verse draws attention to "obey" and "word", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 13's "But ye brethren do not faint in..." into verse 15's "and do not esteem him as an...", so "obey" and "word" belong inside that flow. In 2 Thessalonians context, the local focus is Christ, faith, and discipleship.
A plain takeaway is to answer the verse's own emphasis on "obey" and "word" with trust shaped by these words, not by a vague optimism outside the passage.