Why does Revelation speak of a thousand years?
The thousand years are limited because the Tribulation kills most of the world's population, leaving Gentile believers and a saved Israelite remnant as seed stock. Christ then rules as King in a Kingdom marked by no sin, no death, Satan bound, and ideal conditions, producing a vast population increase.
Les explains that the thousand years must be limited because, as a result of the events of the Tribulation, most of the world's population will lose their lives. Those who become believers through the preaching of the 144,000 will be martyred and resurrected later, but survivors remain. Gentile believers who survive become the seed stock of Gentile nations, while the protected remnant of Israel, saved at Christ's second coming, becomes the seed stock of the nation of Israel. Coming into the Kingdom with Christ ruling and reigning as King, this thousand-year period will be a time of tremendous population growth because there is no sin, no death, Satan is locked up, and there is tremendous prosperity, food production, and ideal climate—like the Garden of Eden—so population increases from both the Gentile nations and Israel.