A millennium is 1,000 years. Revelation 20 describes the 1,000-year rule of Jesus Christ on earth. Christian groups who highly respect Scripture as God's inspired and authoritative word have held three views on how this millennium relates to the second coming of Jesus:
Premillennialism: The time between Jesus' first and second comings will end when he returns. He will rule on earth for 1,000 years with his holy people. After this, Jesus will bring final judgment and establish his eternal kingdom. This view places Jesus' return before (pre-) the millennium.
Amillennialism: This is not a literal 1,000-year period. The "1,000 years" is symbolic and represents the current time between Jesus' first and second comings. During this period, Jesus rules spiritually with his people. At the end of this time, Jesus will return, bring final judgment, and begin his eternal kingdom. This view sees no (a-) separate millennium apart from the current church age.
Postmillennialism: During the time between Jesus' first and second comings, he will extend his rule through the church. This will lead to a long period of peace on earth. This period is the "1,000 years." At the end of this time, Jesus will return, carry out the final judgment, and establish his eternal kingdom. This view places Jesus' return after (post-) the millennium.
These different ideas have caused conflict among Christians. Many have abandoned Christian relations with those who hold different opinions. But Christians should show humility and love, not letting these differences divide them. (see 1 Peter 3:8).
The main message of Revelation is that Jesus Christ will physically return and rule a new heaven and earth. A real spiritual battle is happening. Hell, like heaven, is real, and God will judge everyone by his standards. The prophecies of Revelation give hope to God's people during pain, suffering, and confusion in the world.
Passages for Further Study