When Christ ushers in the millennium at his Second Coming,¹ a great multitude of exalted saints will accompany him.² They will rule and reign with Christ on earth for a thousand years.³ They are kings and queens⁴ that have been sealed in the temple as husbands and wives⁵ in the Patriarchal Order of the Priesthood.⁶ Therefore, they have the seal of the Living God,⁷ and their calling and election is made sure.⁸ They are members of the Church of the Firstborn⁹ and are numbered among the 144,000 Servants that will stand with Christ on heavenly mount Zion at the Second Coming.¹⁰

Once the millennium begins, these 144,000 Servants will fulfill their mission as saviors on mount Zion¹¹ to bring as many as will come to the church of the Firstborn, as revealed in Doctrine and Covenants Section 77:11.¹² This means they will preside over and carry out temple work¹³ for both the living and the dead¹⁴ from all nations, kindreds, tongues, and people.¹⁵ Temples are the only place on earth where vicarious gospel ordinances can be performed for the dead¹⁶ and where exalting ordinances for both the living and the dead can be performed.¹⁷ All gospel ordinances must be performed by mortal people on earth, and the ordinances must be received by each person before he or she can be resurrected to the celestial kingdom.¹⁸

Translated people in a terrestrial state can also receive the earthly ordinances of the gospel for themselves without the assistance of a proxy. If this were not the case, then millions of millennial (terrestrial) mortals would not be able to receive their gospel ordinances without the aid of a mortal (telestial) proxy. Translated people can also administer gospel ordinances. The apostle John exemplified this power when he conferred the Melchizedek Priesthood on Joseph Smith and Oliver Cowedery in the company of Peter and James in 1829, as stated in Doctrine and Covenants Section 27:12.

Temple work during the millennium¹⁹ will be an immense undertaking because countless people have died throughout all ages of the earth without receiving their necessary gospel ordinances.²⁰ The first vicarious temple ordinances for the dead began after the resurrection of Jesus Christ.²¹ However, temple ordinances in the time of Christ for both the living and the dead were short-lived due to the rapid onset of the Great Apostasy.²² Today, temple ordinances occur in great numbers,²³ but there are genealogical limitations due to the lack of accurate records.²⁴ Therefore, vicarious temple work for most people will be performed during the millennium.²⁵ In addition, live temple ordinances will be performed for the many millennial mortals that will live during the millennium,²⁶ including honorable people²⁷ who survive the Second Coming²⁸ and then accept the gospel.²⁹

To facilitate temple work during the millennium, there will be hundreds of operating temples.³⁰ Temple work will be the primary labor of righteous mortals on earth³¹ until the end of the millennium.³² Millennial mortals will be assisted in this work by resurrected people from beyond the veil.³³ Resurrected people will also be active participants in the work of the Lord's kingdom on this side of the veil.³⁴ This open communion between heaven and earth, and between mortals and immortals, will facilitate the vicarious work that must be done on behalf of persons that have or will die at any time before the millennium without first receiving their gospel ordinances.³⁵

Without temple work during the millennium, many of God's worthy children would be left without root or branch.³⁶ This means they would have no part in any family relationship after their death.³⁷ They would not be linked³⁸ by the power of the sealing ordinance³⁹ to their ancestral roots, nor would they be bound⁴⁰ to the branches of their posterity.⁴¹ The sealing power forever connects the roots and branches of everyone from the house of Israel⁴² in the Patriarchal Order of the Priesthood going back to Adam.⁴³ The sealing power restored by Elijah in this dispensation is the priesthood power that binds in heaven all things bound on earth.⁴⁴