The 144,000, as mentioned in Revelation 7:1-8 and 14:1-5, refer to 144,000 Jews that were chosen by God and sealed by Him as His servants, with 12,000 coming from each of the 12 tribes of Israel. In the Left Behind books, their purpose was to evangelize to the world the gospel message about Jesus Christ being the only way of salvation. These first appeared in "Left Behind" and were sealed by God along with other believers in "Soul Harvest".