Satan Loosed at End of Millennium
22 And again, verily, verily, I say unto you that when the thousand years are ended, and men again begin to deny their God, then will I spare the earth but for a little season;
23 And the end shall come, and the heaven and the earth shall be consumed and pass away, and there shall be a new heaven and a new earth.D&C 43:29-31
110 And so on, until the seventh angel shall sound his trump; and he shall stand forth upon the land and upon the sea, and swear in the name of him who sitteth upon the throne, that there shall be time no longer; and Satan shall be bound, that old serpent, who is called the devil, and shall not be loosed for the space of a thousand years.
111 And then he shall be loosed for a little season, that he may gather together his armies.
112 And Michael, the seventh angel, even the archangel, shall gather together his armies, even the hosts of heaven.
113 And the devil shall gather together his armies; even the hosts of hell, and shall come up to battle against Michael and his armies.
114 And then cometh the battle of the great God; and the devil and his armies shall be cast away into their own place, that they shall not have power over the saints any more at all.
115 For Michael shall fight their battles, and shall overcome him who seeketh the throne of him who sitteth upon the throne, even the Lamb.
116 This is the glory of God, and the sanctified; and they shall not any more see death.
Revelation 20:1-3, 7-10
1 And I saw an angel come down out of heaven, having the key of the bottomless pit and a great chain in his hand.
2 And he laid hold on the dragon, that old serpent, which is the Devil, and Satan, and bound him a thousand years,
3 And cast him into the bottomless pit, and shut him up, and set a seal upon him, that he should deceive the nations no more, till the thousand years should be fulfilled; and after that he must be loosed a little season.
7 And when the thousand years are expired, Satan shall be loosed out of his prison,
8 And shall go out to deceive the nations which are in the four quarters of the earth, Gog and Magog, to gather them together to battle; the number of whom is as the sand of the sea.
9 And they went up on the breadth of the earth, and compassed the camp of the saints about, and the beloved city; and fire came down from God out of heaven, and devoured them.
10 And the devil that deceived them was cast into the lake of fire and brimstone, where the beast and the false prophet are, and shall be tormented day and night forever and ever.
George Q. Cannon
When Satan will be bound, he will have no power to tempt the [p.87] children of men. This happy period will cover one thousand years. Then Satan will be loosed again. Why will he be loosed again? Because a generation will arise, some of which in the exercise of their agency will listen and yield to him. Thus he will have power over them. They will become his willing servants. In this way wickedness and all the evils under which the earth now groans will be introduced among men; for whenever men will listen to Satan and exercise their agency in that direction, wickedness flourishes and righteousness lessens. (Gospel Truth, 1:86)