Comforted in the Promise of God's Judgment

This is evidence of the righteous judgment of God, that you may be considered worthy of the kingdom of God, for which you are also suffering—since indeed God considers it just to repay with affliction those who afflict you, and to grant relief to you who are afflicted as well as to us, when the Lord Jesus is revealed from heaven with his mighty angels in flaming fire, inflicting vengeance on those who do not know God and on those who do not obey the gospel of our Lord Jesus.  (2 Thess 1:6-8)

So he means that it is just and right for the lawgiver of righteousness both to reward us for our sufferings for the faith and to exact of the adversaries a penalty for impiety.  This will be at the time of consummation.  Then the Lord will come from heaven, the choirs of angels will precede him, and those invested in the gloom of unbelief will be consigned to inextinguishable fire.  Now, the divine apostle wrote this to comfort with future hope those enduring those dire and awful things.  This is surely the reason he also presented the judgment as fearsome, showing firstly the Judge arriving from heaven, then the power of those ministering to him—namely, angels—and then the form of punishment—namely, consignment to flaming fire.

Theodoret of Cyrus, "The Second Letter to the Thessalonians"