I Thessalonians 3:5

For this cause--Because I know of your "tribulation" having actually begun (Th1 3:4). when I--Greek, "when I also (as well as Timothy, who, Paul delicately implies, was equally anxious respecting them, compare "we," Th1 3:1), could no longer contain myself (endure the suspense)." I sent--Paul was the actual sender; hence the "I" here: Paul, Silas, and Timothy himself had agreed on the mission already, before Paul went to Athens: hence the "we," (see on Th1 3:1). to know--to learn the state of your faith, whether it stood the trial (Col 4:8). lest . . . have tempted . . . and . . . be--The indicative is used in the former sentence, the subjunctive in the latter. Translate therefore, "To know . . . whether haply the tempter have tempted you (the indicative implying that he supposed such was the case), and lest (in that case) our labor may prove to be in vain" (compare Gal 4:11). Our labor in preaching would in that case be vain, so far as ye are concerned, but not as concerns us in so far as we have sincerely labored (Isa 49:4; Co1 3:8).

In this chapter the apostle gives further evidence of his love to the Thessalonians, reminding them of his sending Timothy to them, with the mention of his design therein and his inducements so to do (Th1 3:1-5). He acquaints them also with his great satisfaction at the return of Timothy, with good tidings concerning them (Th1 3:6-10). And concludes with fervent prayer for them (Th1 3:11 to the end).

3:5 Paul was concerned that Satan, the tempter (Mark 1:13; 1 Cor 7:5), had undermined the Thessalonians’ faith (1 Thes 3:2, 6, 8) and rendered his work among them futile (Gal 2:2; Phil 2:16).