What does Hebrews 6:8 mean?

According to the early verses of chapter 6, Christians who wallow in a shallow, immature faith run the risk of "falling away." In context, this means the same thing it did for the nation of Israel in Numbers chapters 13 and 14. There, fear caused Israel to disobey God's command to enter the Promised Land. Rather than destroying them, God put Israel under harsh judgment: forty years of aimless wandering in the desert. Only after this was complete could they resume their progress into Canaan.

This history is used in Hebrews as a warning to saved Christians: those who allow doubt to produce disobedience don't just risk losing their rewards. They also put themselves in line for harsh, cleansing judgment from God. The metaphor of verses 7 and 8 completes a thought begun in verses 1 through 3, and expanded in verses 4 through 6. Those who "fall away," like Israel did, are like a field which receives rain, but only produces weeds. The farmer does not destroy the field, just as God does not damn the fallen believer (1 John 1:9; John 10:28–30). But the only remedy for a thorn-choked field is fire, to burn away the thorns and reset its progress.

In the same way, God's fire and judgment on the fallen Christian does not mean a loss of salvation. Rather, it means experiencing pain and suffering, to prepare us to trust and obey. Those with a "shipwrecked faith" (1 Timothy 1:19–20) might well come back to full faith, after they have suffered. The warning of this passage is to avoid being in that state of "disqualification" (1 Corinthians 9:27).

This verse also helps to distinguish between fields which have always produced large amounts of crops, versus those who have yet to give a significant return. Both are still used by the farmer, and both still receive the rains from God. While the Bible makes it clear that saved Christians produce the "fruit of the Spirit" (Galatians 5:22–23), it does not claim that all Christians are equally productive.

In other words, saved believers all produce the same kind of spiritual fruit, but not the same quantity of spiritual fruit. Those who struggle in their spiritual walk are not necessarily showing signs of being lost. Rather, they might be experiencing a season of judgment preparing them for a more productive future. Where each person is, in terms of their own salvation, is always between them and God alone (1 Samuel 16:7). Human judgment is flawed, so we need to be careful how we use it.