Death is considered by Christians to be a state of separation. In physical death, the spirit God has given to the body has been separated from the body. In spiritual death (called the "second death"), the soul is separated from God for all eternity, cast into the Lake of Fire. Jesus promises to believers that "those who overcome" through faith shall "not be hurt by the second death".
Throughout the Left Behind series, death commonly occurs, both at the hands of humans and as part of God's divine judgments against man. During the Tribulation, the world population is depleted to the point where only one-fourth of that population remained at the time of the Glorious Appearing, and a good deal of that remaining population was sent to the Lake of Fire at the "sheep and goats" judgment.