Answer
Eternal death is the fate that awaits all people who ultimately reject God, reject the gospel of His Son, Jesus Christ, and remain in their sin and disobedience. Physical death is a one-time experience. Eternal death, on the other hand, is everlasting. It is a death that continues through eternity, a spiritual death that involves a separation from God. Just as spiritual life, by grace through faith in Christ (Ephesians 2:8–9), is everlasting, eternal death is never-ending.
Does the Bible teach the doctrine of eternal death? Yes, the Bible clearly teaches an eternal separation of the wicked from God. Here are three passages, one from the Old Testament and two from the New, that support the doctrine of eternal death:
• “And many of those who sleep in the dust of the earth shall awake, some to everlasting life, and some to shame and everlasting contempt” (Daniel 12:2, ESV).
• “And [the wicked] will go away into eternal punishment, but the righteous into eternal life” (Matthew 25:46, ESV).
• “Then Death and Hades were thrown into the lake of fire. This is the second death, the lake of fire. And if anyone’s name was not found written in the book of life, he was thrown into the lake of fire” (Revelation 20:14–15, ESV). Verse 10 emphasizes the perpetual state of torment associated with eternal death, as the lake of fire burns “forever and ever.”
All three of these passages (and more could be added) have as their main context the scene of final judgment. After Jesus Christ returns, three things will occur:
1) The general resurrection
2) The final judgment
3) The inauguration of the eternal state
The fate of the righteous and the wicked could not be more different. The righteous—who are declared righteous on the merits of their Savior, Jesus Christ—will be ushered into a final state of glory. Meanwhile, the wicked—who have rejected Christ—will be sent to the lake of fire for eternal punishment and torment. Note too (particularly in the Daniel and Matthew passages) that the same adjective (everlasting or eternal) is used to modify both life and punishment/contempt. Both the life and the punishment last forever.2) The final judgment
3) The inauguration of the eternal state
The doctrine of eternal death is not a popular one. However, truth is independent of the popular vote. The truth is that, due to our sin, we are under the just condemnation of God. God has sent His Son to die in our place and rise again to reconcile us to God. We can choose to embrace the saving message of Jesus Christ and have forgiveness and eternal life. Or we can decide we don’t need the Son of God, in which case we will perish in our sin and be under God’s judgment. To reject the Source of life is to choose eternal death.