Jamieson, Fausset and Brown on 2 Thessalonians 1:7

7. rest--governed by "to recompense" (2Th 1:6). The Greek is literally, "relaxation"; loosening of the tension which had preceded; relaxing of the strings of endurance now so tightly drawn. The Greek word for "rest," Mt 11:28, is distinct, namely, cessation from labor. Also, He 4:9, "A keeping of sabbath."

with us--namely, Paul, Silas, and Timothy, the writers, who are troubled like yourselves.

when--at the time when ... ; not sooner, not later.

with his mighty angels--rather as the Greek, "with the angels of His might," or "power," that is, the angels who are the ministers by whom He makes His might to be recognized (Mt 13:41, 52). It is not their might, but His might, which is the prominent thought.