Here's some things I found interesting relating to the millennial reign:
Satan will be bound in the bottomless pit for 1000 years. During which time Jesus will rule on earth with the resurrected martyred saints who were killed for refusing to worship the image of the beast and take his mark. At the end of the 1000 years, Satan will be released from the bottomless pit and will go forth to deceive the nations Gog/Magog. (Rev 20). So we have the beast system in power before the millennial reign, then it is removed for the duration of the millennial reign when Satan is in the bottomless pit, then we also have Satan re-emerging from the bottomless pit after the millennial reign to restore his beast system.
In Rev 17 we read "The beast that you saw was, and is not, and will ascend out of the bottomless pit and go to perdition. And those who dwell on the earth will marvel, whose names are not written in the Book of Life from the foundation of the world, when they see the beast that was, and is not, and yet is." Again we see that there will be a time when the beast is in power, but then it will not be in power, and then it will re-emerge after ascending from the bottomless pit. If we look at this in the light of what we have read in Revelation 20, we can place the opening of the bottomless pit at the end of the millennial reign. Therefore both scriptures are in agreement: the beast will be in power (before the millennial), not in power (during the millennial), and will re-emerge (after the millennial).
In Revelation 13 we read "And I saw one of his heads as if it had been mortally wounded, and his deadly wound was healed. And all the world marveled and followed the beast. So they worshiped the dragon who gave authority to the beast; and they worshiped the beast, saying, “Who is like the beast? Who is able to make war with him?” We see here once again that the beast will be in power, then it will be fatally wounded, but it will then it will be restored. We can take what we have learned from Revelation 20 and 17 to understand that the beast will be in power (before the millennial), it will be fatally wounded (for the duration of the millennial), and it will be healed/revived (after the millennial). This makes it easier to understand the reaction of the world at the time of the restoration of the beast system. If the world sees the beast's kingdom restored to power seemingly overcoming Jesus' kingdom, people would be amazed. They would marvel and ask such questions as, "Who is like the beast? Who is able to make war with him?".
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We can now divide the three timeframes from the above scriptures:
The Beast kingdom followed by The Millennial Reign Of Christ followed by The Beast Which Ascends From The Bottomless Pit
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Now we have divided the three timeframes, we can piece together a bit more of the puzzle:
We read in Revelation 9, Then the fifth angel sounded: And I saw a star fallen from heaven to the earth. To him was given the key to the bottomless pit. And he opened the bottomless pit, and smoke arose out of the pit like the smoke of a great furnace. So the sun and the air were darkened because of the smoke of the pit. Then out of the smoke locusts came upon the earth. And to them was given power, as the scorpions of the earth have power. They were commanded not to harm the grass of the earth, or any green thing, or any tree, but only those men who do not have the seal of God on their foreheads. And they were not given authority to kill them, but to torment them for five months. Their torment was like the torment of a scorpion when it strikes a man. In those days men will seek death and will not find it; they will desire to die, and death will flee from them. So we find out here that the sounding of the fifth trumpet will initiate the opening of the bottomless pit. We know that the opening of the bottomless pit will be at the end of the millennial reign. Therefore, the events that take place from the fifth trumpet to the seventh trumpet must be post-millennial reign; during the time of the beast that ascends from the bottomless pit.
We are given confirmation of this in Revelation 11, Then I was given a reed like a measuring rod. And the angel stood, saying, “Rise and measure the temple of God, the altar, and those who worship there. But leave out the court which is outside the temple, and do not measure it, for it has been given to the Gentiles. And they will tread the holy city underfoot for forty-two months. And I will give power to my two witnesses, and they will prophesy one thousand two hundred and sixty days, clothed in sackcloth.” These are the two olive trees and the two lampstands standing before the God of the earth. And if anyone wants to harm them, fire proceeds from their mouth and devours their enemies. And if anyone wants to harm them, he must be killed in this manner. These have power to shut heaven, so that no rain falls in the days of their prophecy; and they have power over waters to turn them to blood, and to strike the earth with all plagues, as often as they desire. When they finish their testimony, the beast that ascends out of the bottomless pit will make war against them, overcome them, and kill them. And their dead bodies will lie in the street of the great city which spiritually is called Sodom and Egypt, where also our Lord was crucified. Then those from the peoples, tribes, tongues, and nations will see their dead bodies three-and-a-half days, and not allow their dead bodies to be put into graves. And those who dwell on the earth will rejoice over them, make merry, and send gifts to one another, because these two prophets tormented those who dwell on the earth. We see here that it is the "beast that ascends out of the bottomless pit" who kills the two witnesses. Therefore this places the time of the two witnesses after the millennial reign, confirming that the events of the fifth trumpet to the seventh trumpet take place after the millennial reign.
I will stop here for now, I hope this blesses someone.