For yourselves, brethren, know our entrance in unto you, that it was not in vain:
For - confirming 1 Thessalonians 1:9. He discusses the manner of his preaching among them (cf. 1 Thessalonians 1:5 and former part of 1 Thessalonians 2:9), from 1 Thessalonians 2:1-12; and the Thessalonians' reception of the word (cf. 1 Thessalonians 1:6-7, and latter part of 1 Thessalonians 2:9), from 1 Thessalonians 2:13-16.
Yourselves. Not only do strangers report it, but you know it to be true (Alford).
Was, х gegonen (G1096)] - rather, 'hath proved:' implying the permanent character of his preaching.
Not in vain - Greek, 'not vain;' i:e., 'full of power' (1 Thessalonians 1:5).