And the devil who deceived them was thrown into the lake of fire and brimstone, where the beast and the false prophet are also; and they will be tormented day and night forever and ever.
Rev. 20:10 NASB
Here is the key to start unlocking how long the lake of fire continues to burn:
Then death and Hades were thrown into the lake of fire. This is the second death, the lake of fire.
Rev. 20:14 NASB
Do death and Hades (the grave) persist forever, or is the message of “lake of fire” that whatever goes into it ceases to exist forever?
Along with Rev. 20:14 pointing to the lake of fire being a destroying force for death, there’s the lake of fire for the beast (Rev. 19:20). The parallel for that is the beast’s being “slain, and its body was destroyed and given to the burning fire” in Dan. 7:11. Like with death, the beast, false prophet and other will be destroyed by the lake of fire.
Now for a look under the hood of the Greek word βάσανος basanos, translated “torment” in Revelation 20:
Elsewhere in the OT basanos denotes means of reparation for guilt (1 Sam. 6:3–4, 8, 17), shame or disgrace (Ezek. 16:52, 54), a cause of sin or misfortune (3:20; 7:19), or God’s punishments (16:52, 54, of Jerusalem; 32:24, 30, of the heathen nations).
New International Dictionary of New Testament Theology
Look particularly at Ezekiel 32:24, 30, which talks about basanos in the grave, in other words, disgrace by being brought low and ended. That’s what will happen to death, the beast and the false prophet in the lake of fire.
Another point is with the phrase in Rev. 20:10 translated “forever and ever.” Because Revelation is rooted deeply and sources heavily from the Hebrew Scriptures, we should look at how those words are used in the Greek translation of the Hebrew (i.e., the Septuagint, what the apostles most often quoted from).
The Greek word translated “forever” in Revelation 20 is αἰών eon. As with basanos for “torment,” Revelation and the rest of the NT takes its cue for meaning from the Hebrew Scriptures. In the LXX (Septuagint), aeon translates with the Hebrew word עולם olam, which is closely linked to the life of the person or thing described.
One must also observe that the NT does not use the phrase ‘eternal death,’ because the idea of eternity is so closely connected with life that the negation of eternal life can also only be understood as the experience of ruin.
New International Dictionary of New Testament Theology
For example, words of God are olam eternal, but the temple is olam only until the One leaves it.
So the disgrace of the lake of fire persists only until the beast and false prophet are destroyed. That’s why the lake of fire is called “the second death” in Rev. 20:14.