Revelation 20:7: And when the thousand years are expired, Satan shall be loosed out of his prison,

In Revelation 20:1-3, Satan is bound in the bottomless pit or depths of hell¹ for the duration of the thousand-year millennium.² Revelation 20:7 describes the end of the millennium when the thousand years are expired and Satan shall be loosed out of his prison for a little season.³ This coincides in time with the end of the terrestrial resurrection and the end of the first resurrection.⁴ The loosing of Satan and the unembodied spirit sons of perdition during the First Woe in Revelation 9:1-12⁵ is a type and foreshadow for the end of the millennium when Satan will again be loosed with all the spirits that have been his unembodied followers since the premortal existence.⁶ The disembodied spirits of mortal sons of perdition will not be loosed with Satan after the millennium. They will be permanently cast into the lake of fire during the Third Woe⁷ at Christ's Second Coming as recorded in Revelation 19:20.⁸

Wickedness will increase toward the end of the millennium⁹ as foreshadowed by the Nephite apostasy at the end of their mini-millennium.¹⁰ The little season after the millennium will be ushered in as Michael uses the keys of the priesthood to loose Satan from the bottomless pit.¹¹ This will empower Satan to muster his armies for the battle of Gog and Magog¹² against Michael and his heavenly hosts.¹³ Satan must be loosed with great power during the little season to fulfill God's purposes,¹⁴ just as Satan must be loosed during the First Woe with great power.

Satan will have great power during the little season because God allows it, and also because wicked people living at that time choose to allow it.¹⁵ Telestial-worthy people and mortal sons of perdition will be the only people alive during the little season because all celestial and terrestrial people will be resurrected by the time the millennium ends.¹⁶ According to Doctrine and Covenants Section 76:103, telestial-worthy people are "liars, and sorcerers, and adulterers, and whoremongers."¹⁷ The mortal sons of perdition are even worse¹⁸ vessels of wrath.¹⁹ This latter group will openly rebel and apostatize²⁰ from Christ's millennial church and kingdom.²¹ Both groups will be so prone to evil that Satan will have his greatest power ever on earth²² and will cause great wickedness during the little season.²³ At this time, Satan will establish his eighth worldly kingdom of seven as described by John in Revelation 17:10-11.²⁴

The spiritual conditions on earth during the little season will be exactly opposite from those of the millennium. During the millennium, Satan will be bound and only people of the celestial and terrestrial kingdoms will live on the earth.²⁵ This is when children grow up without sin unto salvation.²⁶ During the little season, by contrast, Satan will be loosed and only people of the telestial kingdom and sons of perdition will live on the earth.²⁷ The little season is a time of final testing, when the mortals then living will qualify themselves for an inheritance in the telestial kingdom or they will sin unto death and qualify themselves for outer darkness.²⁸ Despite the wicked and telestial-like evils that will then exist, the earth itself will remain physically in a terrestrial or paradisaical condition during the little season.²⁹

The purpose of the little season is to complete the battle for the souls of mankind that began in the premortal existence.³⁰ In this final war on earth,³¹ the Lord will sift the nations of the wicked³² as if they were in a sieve.³³ In this time of great iniquity, the wrath of God will be poured out without measure.³⁴ People who repent will literally suffer the wrath of God on earth to qualify themselves for telestial glory as described in Doctrine and Covenants Section 76:104.³⁵ Those that refuse to repent and willfully rebel will qualify themselves for outer darkness as sons of perdition.³⁶