Albert Barnes Commentary 1 Thessalonians 3:8

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

For now we live, if you stand fast in the Lord. This is equivalent to saying, "My life and comfort depend on your stability in the faith, and your correct Christian walk."

Compare to Martial 6.70: "Non est vivere, sed valere, vita"—"Life consists not merely in living, but in the enjoyment of health." See also Seneca, Epistle 99, and Manilius 4.5, as quoted by Wetstein.

The meaning here is that Paul now enjoyed life; he had that which constituted real life because they acted in a way befitting Christians, thereby showing that his labour among them had not been in vain.

The same thing affirmed here is true of all faithful ministers of the gospel. They feel that they have something that may be called life, and that is worth living for, when those to whom they preach maintain a close walk with God.