In contrast with the troubled existence, conditioned by affliction and distress, that the apostles had been enduring.
If ye stand fast.
For the significance of “stand fast” see on Phil. 1:27. Paul states that so long as the Thessalonians remain steadfast, he and his companions will enjoy life in its fullest Christian sense. Such a heartfelt expression of love and his ardent interest in their eternal welfare must have encouraged the Thessalonians to be faithful.