Please also see this similar question and answer.
Revelation 20:10,14 (KJV), “And the devil that deceived them was cast into the lake of fire and brimstone, where the beast and the false prophet are, and shall be tormented day and night forever and ever…And death and hell were cast into the lake of fire. This is the second death.”
Revelation is a book of symbols; it is not literal. It is a book written to the Christian church, both true and false (Matthew 13) unfolding 2,000 years of church history.
In Revelation 20, Satan is bound for a thousand years, and all mankind is resurrected from the grave (John 5:28,29). During this 1,000-year judgment period, mankind will learn righteousness. It is not an instantaneous judgment. At the end of the thousand years, Satan will be loosed to test mankind to see if they still love sin and evil (verse 3). Those whom Satan can ensnare will permanently be destroyed (Proverbs 2:22).
Some believe verse 10 portrays Satan and his evil angels stoking fires to torture non-believers for all eternity. What a frightful prospect! Even God could not imagine such a thing (Jeremiah 19:5).
If the lake of fire is not a burning hell, what does it represent? First, notice who is thrown into the lake: the devil, the beast and false prophet, “death and hell” and “anyone not found written in the Book of Life.”
What do all of these have in common? They are all enemies of God, which will be destroyed (1 Corinthians 15:26). Even Satan and his evil influence will be destroyed. Ezekiel 28:18-19 (NIV), “By your many sins and dishonest trade you have desecrated your sanctuaries. So I made a fire come out from you, and it consumed you, and I reduced you to ashes on the ground in the sight of all who were watching. All the nations who knew you are appalled at you; you have come to a horrible end and will be no more.” What better way to depict complete and utter destruction than with the symbol of a “lake of fire” and “brimstone”?
The “beast” and “false Prophet” are personifications of human institutions – corrupt religious systems Satan has used to defile God’s truth and keep mankind in bondage and slavery.
“Death and hell” (the grave) will also be in the lake of dire. They go there because the graves are now empty – everyone has been resurrected. When the righteous live forever there will be no more death (Revelation 21:4).
And finally, “Whosoever was not found written in the Book of Life” – these are the individuals who will not pass the final test of loyalty to God. They will be physically perfect, but their hearts will still be in sympathy with Satan. They will go into the lake, which verse 14 tells us is the “second death”—a death with no hope of another resurrection. Psalm 145:20, “all the wicked He will destroy.”
How will those in the lake be “tormented”? This word in the Greek means “touchstone,” a point of reference. They will be an everlasting (forever) example of the terrible results brought about by rebellion against God.
