Revelation 19:20

The Lord Jesus Christ will then cast the beast and the false prophet into the lake of fire alive (cf. Numbers 16:30; Psalms 55:15; 2 Thessalonians 2:8). The description of the false prophet vindicates his punishment. They will still be there 1,000 years later (Revelation 20:10). Thus consignment to the lake of fire does not mean annihilation. The wicked who have died throughout history are not yet in the lake of fire (cf. Matthew 5:22; Matthew 10:28; Matthew 25:41; Mark 9:43; James 3:6). They are in Hades (or "the grave;" cf. Matthew 16:18; Luke 16:23; Acts 2:27), the temporary abode of dead unbelievers before their resurrection. The Valley of Hinnom, or Gehenna, was a foreview of this lake (cf. 2 Kings 16:3; 2 Kings 23:10; Jeremiah 7:31-32; Jeremiah 19:6; Matthew 5:22; Mark 9:43). Neither is the lake of fire "the abyss," which is a temporary place of confinement for angels (Revelation 9:1; Revelation 20:1). At the end of the Millennium, Christ will cast all unbelievers into the lake of fire (Revelation 20:14-15). God originally prepared the lake of fire for Satan and his angels (Matthew 25:41).

"Because no one has yet experienced the lake of fire, it is difficult to portray in human language the awful nature of that punishment. The figure of a burning lake is God’s chosen imagery for visualizing eternity separated from Him. One should remember that figures of speech are always less than the reality, not more!" [Note: Thomas, Revelation 8-22, p. 398.]

Brimstone is a sulphurous material that, united with fire, represents indescribable torment (cf. Genesis 19:24-25; Ezekiel 38:22).

"The fact that in the gospels hell is pictured not only as a place of fire but also as a place of darkness (Matthew 8:12; Matthew 22:13; Matthew 25:30) suggests that both descriptions use metaphorical language drawn from contemporary Judaism to describe final and irremedial [sic] judgment." [Note: Ladd, p. 258.]