“If your hand or your foot causes you to stumble, cut it off and throw it from you; it is better for you to enter life crippled or lame, than to have two hands or two feet and be cast into the eternal fire. 9 “If your eye causes you to stumble, pluck it out and throw it from you. It is better for you to enter life with one eye, than to have two eyes and be cast into the fiery hell,”  (Matthew 18:8–9).

In the context of dealing with conditionalism, Matthew 18:8-9 is worth examining. Ultimately all conditionalists believe that the wicked will be annihilated. They teach that the wicked will eventually stop existing, which is their final punishment. If that is the case, then why is it that Jesus is warning people about being cast into the eternal fire? Is eternal fire the same thing as nonexistence? No, it isn’t.

Generally, the conditionalist position is that eternal fire is eternal because God is eternal (Psalm 90:2), and God is also called a consuming fire (Heb. 12:29). Of course, taking different verses from different places in Scripture and putting them together to make a compound-truth is exegetically risky. Nevertheless, some annihilationists will say that when Jesus was warning people about being cast into eternal fire, he was warning them about the coming judgment of annihilation because, some say, the wicked will undergo a period of fiery torture until they are consumed and stop existing. Not all conditionalists hold to this, but a lot do. Some conditionalists don’t affirm a period of fiery consumption. Some just believe in direct annihilation.

I think the conditionalist analysis of eternal fire is incorrect.  Let me quote from the article Word Study on Eternal Fire

“The phrase “eternal fire” only occurs three times in the entire Bible in the English in the NASB, ESV, ISV, RSV. In the KJV and NKJV, it only occurs in Jude 7. The KJV and the NKJV use “everlasting fire” in Matt. 18:8; 25:41 for a total of three uses. In the Greek, the phrase “eternal fire” consists of two words: “eternal” is αἰώνιος, aiōniŏs and “fire” is πῦρ, pur. “Eternal” occurs 71 times in the New Testament. “Fire” occurs 73 times. The combination of those who Greek words of “eternal fire” only occurs 3 verses: Matt. 18:8; 25:41; Jude 7.

In Matthew 18:8 and Jude 7 the punishment of the wicked is to suffer eternal fire. Of course, the conditionalists will say that the eternal fire that emanates from God eternally because God is a consuming fire (Heb. 12:29).  But in Matthew 25:41 the accursed ones are cast into the eternal fire which “has been prepared for the devil and his angels.” If the eternal fire is something that emanate out of God because God is eternal, then the eternal fire was there forever in order to burn the devil and his angels. But that would not fit with the idea that God is a consuming fire.”

All right as you can see, the phrase “eternal fire” does not occur very often in the Bible. In the places where it does happen, it’s dealing with punishment. What is worth mentioning is that in Matthew 25:41, Jesus said that the eternal fire into which the wicked will depart has been prepared for the devil and his angels. The devil, who is an angel, is cast into the lake of fire along with the beast and the false prophet and will be tormented day and night forever never, (Revelation 20:10). When we consider the fact that angels do not die according to Jesus (Luke 20:36), then the eternal fire is the actual place of continued judgment that the wicked experience without end. To say, as some conditionalist like to maintain, that the eternal fire is eternal because it comes from God, doesn’t make sense.

Conclusion

In Matthew 18:8, Jesus is warning people about suffering the fate of being cast into eternal fire, not because they will stop existing, but because eternal fire is a horrible place. The eternal fire, the “lake of fire,” is a stark and terrifying reality where the unbelievers who have rejected Christ will suffer eternal conscious torment (Rev. 20:15) just as the devil will along with the beast, the false prophet (Rev. 20:10). After all, that fire was prepared for the devil and his angels (Matt. 25:41), and since angels don’t die (Luke 20:36), the eternal fire is eternal in its burning, not in its source. Otherwise, Jesus’ warning doesn’t really have any real threat. The nonexistence of annihilation isn’t anything; it is just ‘nothing.’ There is no suffering in nonexistence. There is no punishment in nonexistence. There’s just nothing. The conditionalist position does not make sense in light of Christ’s words in Matthew 18:8 who warned them not to enter into that eternal fire which will never end.