Why is the Kingdom in Revelation limited to a thousand years?
The Kingdom is limited to a thousand years because the Tribulation will kill most of the world's population, leaving surviving Gentile believers and a saved Israelite remnant as seed stock. That millennial rule lets Christ repopulate the earth under ideal conditions—no sin, death, or Satan—producing a tremendous population explosion.
Les explains that Revelation's thousand-year Kingdom must be limited in time because the Tribulation will drastically reduce the world's population. Most people will lose their lives. Those who believe through the preaching of the 144,000 will be martyred and resurrected later. Still, survivors remain at the end of the seven years; some become believers, predominantly Gentiles, and they will be the seed stock of Gentile nations entering the Kingdom. Also, at the midpoint of the Tribulation, a remnant of Israel goes into the mountains southeast of Jerusalem, as Jesus Himself speaks of in Matthew 24. God protects them for three and a half years, as He cared for Israel forty years in the wilderness. At His second coming, the nation as a whole finally believes, becoming the seed stock of Israel. So the thousand-year period is a time of tremendous population growth, even a population explosion, because there is no sin, no death, and Satan is locked up. It will have tremendous prosperity, food production, and ideal climate—like the Garden of Eden—with great increase from Gentile nations and Israel.