2 Thessalonians 1:8

In flaming fire [ε ν π υ ρ ι φ λ ο γ ο ς]. Lit. in a fire of flame. Comp. 1 Corinthians 1:13; 2 Peter 3:7.

Taking vengeance [δ ι δ ο ν τ ο ς ε κ δ ι κ η σ ι ν]. Lit. giving or rendering. Vengeance is an unfortunate rendering, as implying, in popular usage, personal vindictiveness. See on 2 Corinthians 7:11. It is the full awarding of justice to all parties.

On them that know not God - obey not the gospel [τ ο ι ς μ η ε ι δ ο σ ι θ ε ο ν - τ ο ι ς μ η υ π α κ ο υ ο υ σ ι ν τ ω ε υ γ γ ε λ ι ω]. To know God is to know him as the one, true God as distinguished from false gods; to know his will, his holiness, his hatred of sin, and his saving intent toward mankind. Two words are used of such knowledge, eiJudenai and ginwskein. Both are applied to the heathen and to Christians, and both are used of the Jews ' knowledge of God. Eidenai, of heathen, Galatians 4:8; 1 Thessalonians 4:5; 2 Thessalonians 1:8. Ginwskein of heathen, Romans 1:21; 1 Corinthians 1:21. Eidenai, of Christ and Christians, John 7:29; John 8:19; John 8:55; John 14:7. Ginwskein of Christ and Christians, Galatians 4:9; 1 John 2:13; 1 John 2:14; 1 John 4:6; 1 John 4:7; 1 John 4:8; John 10:15; John 17:3. In John, ginwskein of Jews who do not know the Father, John 16:3; John 8:55 : eiJudenai, John 7:28; John 8:19; John 14:21. The two are combined, John 1:26; John 7:27; John 8:55; 2 Corinthians 5:16. A distinction is asserted between ginwskein as knowledge grounded in personal experience, apprehension of external impressions - and eiJudemai purely mental perception in contrast with conjecture or knowledge derived from others. There are doubtless passages which bear out this distinction (see on John 2:24), but it is impossible to carry it rigidly through the N. T. In the two classes, - those who know not God and those who obey not the gospel, - it is not probable that Paul has in mind a distinction between Jews and Gentiles. The Jews were not ignorant of God, yet they are described by John as not knowing him. The Gentiles are described by Paul as knowing God, but as refusing to glorify him as God (Romans 1:21). Paul rather describes here the subjects of God's judgment as one class, but under different aspects.