Charles Ellicott Commentary 1 Thessalonians 3:8

"for now we live, if ye stand fast in the Lord." — 1 Thessalonians 3:8 (ASV)

Now we live, if.—“Now” contrasts the new life and vigor which the “gospel of their faith and charity” had infused into the Apostle, with the deadly sinking he had felt at the thought of their possible apostasy. At the same time, the “if” has the half-future sense, as if St. Paul meant that the continuance of this “life” was contingent upon their continued steadfastness.

Another interpretation has been suggested, according to which both the “we” and “you” are perfectly general, and therefore interchangeable, and the sense is made to be a vague proposition, “for standing fast in the Lord is a sine qua non of life”—life in the theological sense: and parts of Romans 7:8 are compared. This interpretation, however, suits the Greek as little as the context.