Why do some passages say that those who are rejected by Jesus Christ will be cast into a lake of fire?

Revelation 20:14 tells us that the lake of fire is the same as the second death. Men use fire to destroy rubbish. In the Bible, God speaks of fire in a kind of parable, to show that those whom He finds worthless will be completely destroyed. (See Psalm 37:20; Psalm 68:2; Matthew 3:11-12; 2 Thessalonians 1:7-9). (See also the topic on ‘Hell’ for more).