The second death mentioned in Revelation refers to eternal separation from God and torment in the lake of fire, experienced by those who reject Jesus Christ as their Savior, whereas believers in Christ are promised eternal life and victory over sin and death.
The Reality of Physical Death
Because of the fall of Adam and Eve in the Garden of Eden at the beginning of time, one of the curses that came from this fall was physical death. The Apostle Paul tells us in Romans 5:12 that sin entered the world through Adam's sin, and his sin brought death to everyone. Since the time of Adam, one out of one dies physically. No one has or will ever escape physical death. It is one of the unintended consequences of Adam's sin in the Garden of Eden.
The Eternal Nature of the Spirit
The Apostle Paul says in 1 Corinthians 15:50 that the physical body cannot inherit the Kingdom of God. These dying bodies cannot inherit what will last forever. What lasts forever is the spirit that lives inside each person, the very spirit God breathed into Adam when He made him a living being. This spirit part of each human will live forever somewhere.
The Apostle Paul says in 2 Corinthians 5:1 that when each person dies, their earthly tent is taken down; that is, each person leaves their physical body and receives the heavenly body God has for them.
The Transformation of Believers
But not everyone will experience this transformation! The Apostle Paul also says in 1 Corinthians 15:3 that Christ died for everyone's sins, was buried, and was raised from the dead on the third day. This enabled Christ Jesus to take away the penalty of eternal death.
The Apostle Paul says in 1 Corinthians 15:20 that Jesus was raised from the dead and has become the first fruit of a great harvest of all who have died physically. Meaning this, Jesus' death took away eternal damnation to the soul, but it did not take away the curse of the physical body. Why is that? Because the physical body is sinful, and sinfulness cannot inherit eternal life.
Jesus had to die physically and spiritually. He had to become sinful so that everyone who was sinful could become the righteousness of God. His resurrection defeated death, hell, and the grave. It stole the keys of eternity from the Devil.
The Apostle Paul says in 1 Corinthians 15:53-54 that everyone's dying body has to be transformed into bodies that will never die, and then the Scriptures will be fulfilled, which says, "Death is swallowed up in victory." Everyone who claims the name of Jesus will experience eternal life. Every one of them will receive a new body in the new heaven.
The Fate of Those Who Reject Christ
But what about those who refuse to accept Jesus as their Savior? What happens to them?
Revelation 21:8 says, "But cowards, unbelievers, the corrupt, murderers, the immoral, those who practice witchcraft, idol worshipers, and all liars–their fate is in the fiery lake of burning sulfur. This is the second death."
What is the Second Death?
What is the second death? It is what is reserved for all who don't put their faith and trust in Jesus Christ but decide to go to eternity alone and see if their merit can get them into heaven. As we see in Revelation 21:8, the list eliminates everyone but Jesus. Everyone has lied. Maybe some of the other things on that list are not true for everyone, but lying is true for all except Jesus. He never lied.
So, what is the second death specifically?
This term is mentioned four times in the Book of Revelation. It is mentioned in Revelation 2:11, 20:6, 20:14, and 21:8. John says that in Revelation 2:11, those who are victorious through Jesus will not experience the second death. So, first off, whatever the second death is, no one who is victorious through Jesus will face it. This goes back to the acceptance of Christ as one's Savior, believing He is God and He died for everyone's sin.
In Revelation 20:6, John says that those who share in the first resurrection will not face the power of the second death. The first resurrection is for all believers who have died before the Second Coming of Jesus. So, once again, anyone who believes in Jesus will not face the Second Death, whatever it is.
The Path to Escape the Second Death
Then John says in Revelation 20:14 that death and the grave were thrown into the lake of fire, the second death. And anyone whose name was not found recorded in the Book of Life was thrown into the lake of fire. So, the second death then is eternal physical and eternal spiritual separation from God and constant torment for those who refuse to accept Jesus as their Savior, Lord, and God. Thus, their fate is the fiery lake of burning sulfur.
The only way for a human to escape the second death and the lake of fire is through Jesus. But how does this occur?
The Apostle Paul tells everyone in 1 Corinthians 15:43 that everyone's body, the physical body, is planted in the ground when they die, but through believing in the resurrection of Jesus, they will be raised to life forever as spiritual bodies through the finished work of Jesus Christ on the cross. Jesus gives victory over sin and death.
Responsibilities of Believers While Awaiting Transformation
So, what do people who have accepted Jesus do while they wait for the transformation of their bodies so that they can avoid the second death? The Apostle Paul explains in 2 Corinthians 5:10 that all believers in Jesus must stand before Christ to be judged. Each will receive whatever they deserve for the good or evil they have done in this earthly body.
Until this transformation occurs, the focus is on putting to death the deeds of the flesh and living according to the spirit by walking with the Spirit and keeping in step with the Spirit. Each believer doesn't just do what God asks them to do but does it when He asks them to. This is a dance that is perfected over time.
The Call to Share the Good News
The Apostle Jude tells us there are two primary responsibilities of the believer who has accepted Jesus as their Savior. Jude says believers are to build each other up in the most holy faith by praying in the power of the Holy Spirit and awaiting the mercy of Jesus Christ, who will bring each to eternal life.
Not only is the believer to grow in their ability to do what and when God asks them to do these things, but Jude says to work to "snatch others from the fire." God wants His children to let others know about the Second Death, and through accepting Jesus, they don't have to ever go there.
That's Good News!