Albert Barnes Commentary 2 Thessalonians 1:8

"rendering vengeance to them that know not God, and to them that obey not the gospel of our Lord Jesus:" — 2 Thessalonians 1:8 (ASV)

In flaming fire. This is a circumstance that is not noticed in the account of His appearing in the parallel passage in 1 Thessalonians 4:16. The object of the apostle here seems to be to represent Him as coming amid vivid flashes of lightning. He is commonly described as coming in clouds, and to that common description there is here added the image of incessant lightning, as if the whole heavens were illuminated with a continuous blaze.

Taking vengeance. Margin: yielding. Greek: giving. The word vengeance is used in the sense of punishment, for there cannot be in God what literally corresponds with the human passion of revenge. .

On them that know not God. On all who are strangers to Him; that is, who are living in pagan darkness, or who, having heard of Him, have no practical acquaintance with Him.

And that obey not the gospel of our Lord Jesus Christ. This refers to those who do not embrace it and practice its precepts in their lives. .