One very important purpose of the Millennial Kingdom is to fulfill God’s yet-unfulfilled promises to Israel. In fact, every unconditional covenant God made with Abraham and Israel will be fulfilled in the Millennial Kingdom. Without this future period of time, many of God’s promises would fall to the ground. For instance, the land He promised Abraham extended from the Euphrates River on the east to “the River of Egypt” on the west, but Israel has never occupied all the land God promised her, even at the height of Joshua’s conquest or Solomon’s rule. In the future, she will.
Another purpose of the Millennial Kingdom is to demonstrate for all time that even with Satan bound, Christ governing the earth and millions of believers in their new bodies living thereupon, unregenerate man’s nature will always leave him susceptible to deception, unthankfulness and rebellion. Scripture tells us that as soon as Satan is “let out of jail,” he is able to round up an enormous army and lead another rebellion against God and Christ. All through history there have been some people who believed, and some who did not. This is not due to wealth or lack of it, health or lack of it, education or lack of it, or any other circumstance. One of the amazing things history teaches is that some people make a decision to believe God, and some do not. The Millennial Reign of Christ will be the ultimate proof of that. With health, peace, prosperity and justice over all the earth, some people will still choose not to believe. Not one soul will be able to stand at the Final Judgment and say that if his circumstances had been better, he would have believed. After the Final Judgment, mankind will be thoroughly purified for entrance into the Final Paradise, with no more internal or external vulnerability to sin.