The Millennium is a term that refers to the time when Jesus will personally reign over the entire earth for a period of one thousand years (see Rev. 20:3, 5, 7), which occurs after the seven-year Tribulation. Isaiah foresaw Christ’s governmental reign over the earth almost three thousand years ago:
For a child will be born to us, a son will be given to us; and the government will rest on His shoulders; and His name will be called…Prince of Peace. There will be no end to the increase of His government or of peace, on the throne of David and over his kingdom, to establish it and to uphold it with justice and righteousness from then on and forevermore (Is. 9:6-7, emphasis added).
Similarly, the angel Gabriel announced to Mary that her Son would reign over a never-ending kingdom:
And the angel said to her, “Do not be afraid, Mary; for you have found favor with God. And behold, you will conceive in your womb, and bear a son, and you shall name Him Jesus. He will be great, and will called the Son of the Most High; and the Lord God will give Him the throne of His father David; and He will reign over the house of Jacob forever; and His kingdom will have no end ” (Luke 1:30-33, emphasis added).
During the Millennium, Jesus will personally reign from Jerusalem’s Mt. Zion, which will be raised in elevation above its present height. His rule will be one of perfect justice for all nations, and there will peace over the whole earth:
In the last days, the mountain of the house of the Lord will be established as the chief of the mountains, and will be raised above the hills; and all the nations will stream to it. And many peoples will come and say, “Come, let us go up to the mountain of the Lord, to the house of the God of Jacob; that He may teach us concerning His ways, and that we may walk in His paths.” For the law will go forth from Zion, and the word of the Lord from Jerusalem. And He will judge between the nations, and will render decisions for many peoples; and they will hammer their swords into plowshares, and their spears into pruning hooks. Nation will not lift up sword against nation, and never again will they learn war (Is. 2:2-4).
Zechariah predicted the same:
Thus says the Lord of hosts, “I am exceedingly jealous for Zion, yes, with great wrath I am jealous for her.” Thus says the Lord, “I will return to Zion and will dwell in the midst of Jerusalem. Then Jerusalem will be called the City of Truth, and the mountain of the Lord of Hosts will be called the Holy Mountain”….Thus says the Lord of hosts, “It will yet be that peoples will come, even the inhabitants of many cities; and the inhabitants of one will go to another saying, ‘Let us go at once to entreat the favor of the Lord, and to seek the Lord of hosts; I will also go.’ So many peoples and mighty nations will come to seek the Lord of hosts in Jerusalem and to entreat the favor of the Lord.” Thus says the Lord of hosts, “In those days ten men from the nations of every language will grasp the garment of a Jew saying, ‘Let us go with you, for we have heard that God is with you'” (Zech. 8:2-3, 20-23).
The Bible teaches that believers will actually be ruling and reigning with Christ during those one thousand years. Their level of responsibility in His kingdom will be based upon their faithfulness now (see Dan. 7:27; Luke 19:12-27; 1 Cor. 6:1-3; Rev. 2:26-27; 5:9-10; and 22:3-5).
We will be clothed in our resurrected bodies, but there will apparently be natural people living in mortal bodies who will populate the earth at that time. Furthermore, it seems that the longevity of the patriarchs will be restored, and that wild animals will lose their ferocity:
I will also rejoice in Jerusalem, and be glad in My people; and there will no longer be heard in her the voice of weeping and the sound of crying. No longer will there be in it an infant who lives but a few days, or an old man who does not live out his days; for the youth will die at the age of one hundred. And the one who does not reach the age of one hundred shall be thought accursed….The wolf and the lamb shall graze together, and the lion shall eat straw like the ox; and dust shall be the serpent’s food. They shall do no evil or harm in all My holy mountain. (Is. 65:19-20, 25; see also Is. 11:6-9).
There are many references to the future Millennium in the Bible, especially in the Old Testament. For further study, see Is. 11:6-16; 25:1-12; 35:1-10; Jer. 23:1-5; Joel 2:30-3:21; Amos 9:11-15; Mic. 4:1-7; Zeph. 3:14-20; Zech. 14:9-21; and Rev. 20:1-6.
Many of the Psalms also apply prophetically to the Millennium. For example, read this passage of Psalm 48:
Great is the Lord, and greatly to be praised, in the city of our God, His holy mountain. Beautiful in elevation, the joy of the whole earth, is Mt. Zion in the far north, the city of the great King. God, in her palaces, has made Himself known as a stronghold . For, lo, the kings assembled themselves, they passed by together. They saw it, then they were amazed; they were terrified, they fled in alarm. Panic seized them there, anguish, as of a woman in childbirth (Ps. 48:1-6, emphasis added).
When Jesus sets up His administration in Jerusalem at the beginning of the Millennium, apparently many of the rulers of the earth who survive the Tribulation will hear the report of Jesus’ reign and will travel to see it for themselves! They will be shocked by what they see.
For other Psalms that refer to the millennial reign of Christ, see Ps. 2:1-12; 24:1-10; 47:1-9; 66:1-7; 68:15-17; 99:1-9; and 100:1-5.
 This scripture illustrates how easy it can be to make a wrong assumption about the timing of prophetic events by reading into what scripture actually says. Mary could have easily and logically assumed that her special Son would be reigning on David’s throne within a few decades. Gabriel told her she would give birth to a son who would reign over the house of Jacob, making it sound as if Jesus’ birth and reign would be two seamless events. Mary would never have imagined that there would be at least 2,000 years between them. We also should be cautious of making similar assumptions as we try to interpret prophetic scripture.
 From looking at other scriptures, it seems that the Millennium will begin, not only with believers populating the earth, but with unbelievers as well (see Is. 2:1-5; 60:1-5; Dan. 7:13-14).