Charles Ellicott Commentary 2 Thessalonians 3:7

"For yourselves know how ye ought to imitate us: for we behaved not ourselves disorderly among you;" — 2 Thessalonians 3:7 (ASV)

For justifies the assertion that they had received a better teaching (Compare to 1 Thessalonians 2:1; 1 Thessalonians 4:9; 1 Thessalonians 5:2).

To follow us—The word, of course, means “to imitate.” This rather compressed expression seems to stand for a more complete thought, such as: “You yourselves know how you ought to live, for you only have to imitate us; you remember not only a tradition but also an example.” This is a better reading than Chrysostom's, which suggests the entire “tradition” consisted of example without precept, however much that interpretation might simplify the logic.

For (or because)—This offers a historical justification for the statement that their example was a trustworthy model in this particular respect. You can see the same use of “for” in 1 Thessalonians 2:9, in the phrase “for labouring,” and in 1 Thessalonians 4:3.

It is perhaps simpler, however, to translate the word as “that” instead of “for”: “You know perfectly how to live—how to imitate our example—that we never...” Then follows a description of the Apostles’ conduct at Thessalonica similar to that in the First Epistle. This gives us a clearer understanding of why they dwelt so long and so passionately on the topic there—namely, to shame the disorderly brothers into imitation by the force of a silent contrast.