Expositor's Bible Commentary Commentary 1 Thessalonians 3:5

"For this cause I also, when I could no longer forbear, sent that I might know your faith, lest by any means the tempter had tempted you, and our labor should be in vain." — 1 Thessalonians 3:5 (ASV)

In this situation, Paul, speaking now only of himself at this point, was constrained to find out through Timothy the state of their faith. He knew that “the tempter” (i.e., Satan; cf. Matthew 4:3) had been at work among them and that God permits the enemy this activity. What Paul did not know about the Thessalonians, however, was whether or not the tempter’s solicitations had been successful, making his work and that of his colleagues “useless.”