What does Mark 9:48 mean?

This text, which in some translations is also found in Mark 9:44 and 46, is a quote from Isaiah 66:24. The passage describes a future time when God will gather His people to Jerusalem and they will worship God for eternity (Isaiah 66:18–23). Those who are not His will face everlasting destruction and torment, metaphorically described as the worm and the fire.

"Worm" is from the Greek root word scolex and refers to a maggot that eats dead flesh. The fact that it does not die suggests a different meaning, although scholars are not sure what. Both this verse and Isaiah 66:24 say "their worm," meaning it may be something the unbeliever brought with them, perhaps their shame and regret.

Annihilationism is the belief that after God's final judgment, unbelievers will cease to exist. This is one of the verses that demonstrates this belief is unbiblical. The worm does not die and the fire is not quenched. It may bring comfort to think our non-Christian loved ones will be spared eternal torment, but God made our souls to be eternal.

At the same time, this verse points out God's tremendous grace. Isaiah 66:24 describes the deserved fate of God's enemies. It would be better to die or be maimed than to suffer this fate (Mark 9:43–47), but in reality, none of those preventative measures could ever make us righteous enough to deserve heaven. It is only through the sacrifice of Christ and the grace of God that we can be saved (Romans 3:23; 6:23; Ephesians 2:8–9).