The warning passages in Hebrews are notoriously difficult to interpret. Many have trouble accepting that the warnings were written to believers because of the severe judgments which are threatened, especially the mention of fire, which for many evokes the imagery of hell. Proof that the author of Hebrews wrote to believers in Christ is overwhelming (See GraceNotes no. 15, "Interpreting Hebrews"). Since the warnings are to believers, they could not be threatened with hell, for believers can not lose their salvation (See GraceNotes no. 11, "Eternal Security"). What then do the three references to fire in the warning judgments (6:8; 10:27; 12:31) mean to believers?
Fire signifies many things in the Bible, including hell, but by no means should fire automatically be interpreted as eternal hell fire. Fire is often used in reference to God's people. Sometimes it is the fire of God's wrath that disciplines His people (Num. 11:1-3; Isa. 9:19; 10:17; 29:6; 42:25; Jer. 11:16; 15:14; 17:4; Lam. 2:3-4; 4:11; Eze. 22:20-22; Amos 2:5; Obad. 18; Ps. 78:21; 80:16). Sometimes it refers to a cleansing or purifying trial or judgment (Ps. 66:12; Zech. 13:9; Mal. 3:2; John 15:6; 1 Cor. 3:13-15; 1 Peter 1:7). It was used to picture God's jealousy for the devotion of His people (Deut. 4:24; Ps. 79:5; Zeph. 1:18; 3:8). Fire is also associated with the work of the Holy Spirit (Matt. 3:11/Luke 3:16; Acts 2:3).
We will restrict this study to that which pertains to fire in the warnings of Hebrews, though many other interpretive details would support that fact that the fire mentioned is not eternal hell fire. Notably, eternal fire, eternal torment, hell, and Gehenna are never mentioned in the warnings.
Using an analogy, this warning compares someone who falls away from the Christian faith with earth that receives rain and produces thorns and briers instead of fruit. Such earth is "rejected and near to being cursed, whose end is to be burned." The word "rejected" (adokimos) means to be disqualified and is used of believers in the New Testament in reference to losing future rewards (cf. 1 Cor. 9:27), but is never used of hell. This earth (unfruitful believers) is disqualified from usefulness and the accompanying benefits. Note also that the earth is near to being cursed, not actually cursed. This denotes the seriousness of the apostasy (6:6), but stops short of a total rejection. When it says that the earth is to be burned, one correctly pictures the thorns and briers being burned off the earth, because earth itself cannot burn. Thus it pictures a fire of judgment and/or purging that burns up that which is useless (cf. John 15:6; 1 Cor. 3:13-15). These believers were in danger of becoming "sluggish" (6:12), and such spiritual lethargy would be useless to God and others. God's disciplining judgment has the purpose of making believers holy and fruitful (12:10-11). There seems to be an intended relationship of this warning to Isaiah 5:1-7 which warned Israel that God would burn her for being an unfruitful vineyard. The warning of Hebrews 6 shows that believers who do not go forward with their faith squander God's blessings so that what is produced is not useful but useless and fit only to be discarded, or burned.
The believer who sins willfully (note that the author includes himself as a possibility by using "we") has in store "a certain fearful expectation of judgment, and fiery indignation which devours the adversaries." The willful sin in Hebrews is turning back to sinful Judaism which would be tantamount to giving one's approval to the crucifixion of Jesus Christ.
We first note that God's discipline of believers can be fearful. In Acts 5 when Ananias and Sapphira were struck dead by God because they lied, "great fear came upon all the church" (5:11). One judgment Christians face is the judgment seat of Christ (Rom. 14:10-12; 1 Cor. 3:11-15; 2 Cor. 5;10) which can be a fearful prospect for those who have not lived well (2 Cor. 5:11). The "fiery indignation" (literally "fiery zeal") is that "which will devour the adversaries." This could either mean that the judgment that sinful believers face is of the kind of zealous judgment God intended for His adversaries, or it could mean that the zealous judgment God uses against His adversaries will be used against believers. We have seen how fire was used against God's people in the Old Testament, so either meaning is possible. The "worse punishment" of verse 28 is compared to those who were executed for breaking Moses' law. Is there a punishment worse than death? Absolutely (cf. Lam. 4:6, 9). Suffering in this life can be so terrible that some people kill themselves to find relief.
That this is a judgment on God's people is made clear in verse 30 by the quote from Deuteronomy 32:35-36: "The Lord will judge His People." Furthermore, verse 31 says "It is a fearful thing to fall into the hands of the living God," but at least they will be in His hands. Finally, the contrast between "destruction" (apoleian, or "ruin") and "saving of the soul" (literally, "preserving of the life") in verse 39 could speak of physical life and death or contrast a ruined life with a life that is delivered from the consequences of a negative judgment.
This warning which mentions fire is meant to picture the terrible consequences that believers face if they should willfully turn away from Jesus Christ. The consequences are spiritually devastating, even more painful than death, but eternal hell is not mentioned. The readers, Hebrew Christians being tempted to re-identify with sinful Israel, might also understand this as a warning about the impending national judgment of a fiery destruction of Jerusalem which occurred only a short time later (A.D. 70), something they would know about from Jesus' warnings (Matt. 23:27 - 24:2; Mark 13:1-2; Luke 21:5-6; cf. Acts 2:40).
That "our God is a consuming fire" is a motivation to practice gracious godly reverence in God's service, which was mentioned in the previous verse (v. 28). It is not meant to be a threat of hell, because verse 28 speaks confidently of the readers "receiving a kingdom" in the future. This metaphor of God as a consuming fire comes from Deuteronomy 4:24 where it speaks of God's jealousy.
The judgment of fire in Hebrews refers to God's discipline which can be very severe. Such discipline will be meted out in this life in the form of painful experiences. It is very possible that the fire here would be understood by these Hebrew Christian readers as the fiery destruction of Jerusalem which happened a short time after this book was written, a judgment on Israel for rejecting and crucifying Jesus Christ. In any case, believers don't need to fear burning in hell, but they will experience God's burning anger if they willfully turn away from the benefits of the eternal salvation which Jesus Christ provided through His death and resurrection.