giving vengeance to those who don't know God, and to those who don't obey the Gospel of our Lord Jesus,
It is possible that the expression, those who do not know God, refers to the pagan world (Jeremiah 10:25; 1 Thessalonians 4:5). "They did not see fit to acknowledge God" (Romans 1:28). Theirs was a wilful refusal to know God (Romans 1:18-32); compare (Ephesians 4:18-19). It is possible that a second group is designated as "those who do not obey the gospel (1 Peter 4:17). Some see in this a reference to the Jews. However, it its not certain that Paul had two distinct groups in mind. It may be that Paul is employing Hebrew parallelism. The passage could be translated: "those who do not know God, even upon those who do not obey the gospel." Jesus accused certain Jews of not knowing God (John 8:55) and Paul spoke of the Gentiles as being disobedient (Romans 11:30). It is not a certainty, then, that Paul had two distinct groups in mind. Or, if he did, it is not certain that he referred, in the first, exclusively to Gentiles and, in the second, exclusively to Jews. Paul later spoke of "those who are to perish" as one group (2:10). The principal truth is not affected by the view one takes. The Lord will take vengeance upon those who do not know God; he will take vengeance upon those who do not accept the Lord in gospel obedience (145).