Question: "What does it mean that hell is referred to as a lake of fire?"
Answer: The lake of fire is a term used in only a few verses near the end in the book of Revelation (Revelation 19:20; 20:10, 14, 15; 21:8). Jesus refers to Gehenna/hell several times (Matthew 10:28; Mark 9:43; Luke 12:5), as well as an “outer darkness” (Matthew 8:12; 22:13). These all seem to be different references to the same thing. Hell, the lake of fire, and outer darkness are all terms describing the final destination of those who reject Christ. This is a state of complete separation from God, never-ending and inescapable.
According to the Bible, the lake of fire is the “second death.” This is the ultimate consequence of sin, which is to be totally cut off from God. The lake of fire will be a place of perpetual suffering and misery. Scripture indicates that every person whose name is not in the Book of Life will be cast into the lake of fire (Revelation 20:15). The lake of fire will also be the fate of the beast and false prophet from the end times (Revelation 19:20), as well as Satan himself (Revelation 20:10). The Bible indicates that both death and Hades—the temporary destination of the unsaved dead—will also be cast into the lake of fire (Revelation 20:14).
Even though hell is described using terminology such as fire and flame, it is not meant to be thought of as “only” a physical place. Hell is described as a place of “torment,” not “torture,” initially intended for purely spiritual beings (Matthew 25:41). In fact, the worst aspect of hell is an eternity of conscious, guilty, shameful separation from God and all forms of goodness. In that sense, hell is far worse than a literal inferno; a purely physical hell is actually not as terrible as what the Bible describes.
In other words, the Bible tells us what hell is “like,” using symbols such as the lake of fire. But Scripture does not tell us too much about what hell “is,” in direct terms.
Fire is often used as a symbol of God’s judgment. The symbolism stems from real-life examples of God’s use of fire to punish the wicked—the overthrow of Sodom and Gomorrah (Genesis 19:24), for example, and the destruction of Elijah’s enemies (2 Kings 1:12). Prophets often described God with a stream of fire coming from His throne, a symbol of His holy punishment of sin (e.g., Daniel 7:10; Isaiah 30:33). The fact that the destiny of those who reject God is described as a “lake of fire” speaks to how serious the judgment is. When God finally abolishes sin and death, all sinners will be condemned to the worst possible fate, described in the Bible using the most horrific terms.