What does Hebrews 10:39 mean?

Here, again, the writer of Hebrews speaks with encouragement and a positive tone. The overall theme of the book of Hebrews is that God has given us a superior "new" covenant, in Jesus Christ, to replace the inferior, "old" covenant of animal sacrifice. This has been made plain enough that believers should be confident and steadfast in their faith, even in the face of hardship. Those who succumb to fear and doubt, though they are still saved, are subject to God's punishment and wrath. A living example of this is the nation of Israel, which "shrank back" from the conquest of Canaan and was dealt with harshly as a result (Hebrews 3:12–19).

The Greek of this passage is somewhat more clearly understood than English translations. The phrasing used here is different from what the writer uses to imply eternal salvation. So, the comment about those who "preserve their souls" is not a comment on eternal security. Rather, it seems to be a reference to the person's closeness with God, in terms of the overall spiritual health and well-being, in contrast to those who are faithless. Once again, context matters, and the example given earlier of Israel in the wilderness is key.

This verse speaks to the readers—persecuted Jewish Christians—with an optimistic tone. Those who "hold fast" to their faith don't have to worry about the fiery judgment God has in store for those who willingly rebel against His will (Hebrews 10:26–29).