For justifies the assertion that they had received a better teaching. (Comp. 1 Thessalonians 2:1; 1 Thessalonians 4:9; 1 Thessalonians 5:2.)
To follow us. — The word, of course, means “to imitate”; and the rather compressed expression seems to stand for something fuller, such as, “Yourselves know how you ought to live, for you have but to imitate us: you recollect not only a tradition, but an example.” This is better than (with St. Chrysostom) to make the whole “tradition” consist of example without precept, however such an interpretation might simplify the logic.
For (or because). — Historical justification of the statement that their example was a trustworthy mode in this particular, at any rate: see the same use of “for” in 1 Thessalonians 2:9, “for labouring,” &c.; 1 Thessalonians 4:3. It is perhaps simpler, however, to translate the word “that,” instead of “for “: “You know perfectly how to live — how to imitate our example — that we never,” &c. Then follows a description of the Apostles’ conduct at Thessalonica similar to that in the First Epistle, thus giving us a clearer understanding why they dwelt so long and so passionately upon the topic there — namely, in order by force of tacit, contrast to shame the disorderly brethren into imitation.