This lake was earlier referenced in Revelation 19:20 (see on that text). It describes hell with its endless burning of God’s everlasting wrath on rebellion against him. This place stands in radical contrast to the harmony and bliss that comes with living in the presence of God himself (Revelation 21:3, Revelation 21:7).
8 But as for the cowardly, the faithless, the detestable, as for murderers, the sexually immoral, sorcerers, idolaters, and all liars, their portion will be in the lake that burns with fire and sulfur, which is the second death.”