1:8 flaming fire. This fire may be the same as “the pillar of fire” that protected and guided God’s people in the wilderness (Exodus 13:21). Alternatively, there are numerous references to fires in the tribulation period (e.g., Revelation 8:5-10; 18:8). Finally, climaxing the day of the Lord, the earth itself will be “burned up” (II Peter 3:10).

1:8 vengeance. “Taking vengeance” does not here imply taking revenge but rather exacting justice. God has been long-suffering, but “our God is a consuming fire” and “it [will be] a fearful thing to fall into the hands of the living God” (Hebrews 12:29; 10:31).

1:8 know not God. Knowing God means more than knowing about God; it means knowing Him as He is, personally and reverently acknowledging Him as sovereign Creator, redeeming Savior, and all-seeing Judge.

1:8 obey not the gospel. It is the gospel by which men are saved (I Corinthians 15:1-2) and there can be no other way of salvation (John 14:6; Acts 4:12). The gospel is good news and salvation is offered freely to anyone who will receive it through faith in Christ. There is no acceptable excuse for rejecting His love and sacrificial death. For those who do reject Him, however, “there remaineth no more sacrifice for sins, But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries” (Hebrews 10:26-27).