The Encyclopedia of Mormonism – Elijah, Spirit of

‍https://eom.byu.edu/index.php/Elijah,_Spirit_of  

Author: Finlayson, Mary

For members of The Church of Jesus Christ of Latter-day Saints, the spirit of Elijah is the spirit of family kinship and unity. It is the spirit that motivates the concern to search out ancestral family members through family history; and, on their behalf, to perform proxy baptisms, temple endowments, and sealing ordinances (Hc 6:252). This is seen as fulfillment of the prophecy of Malachi that in the last days Elijah "will turn the heart [in Hebrew, the innermost part, as the soul, the affections] of the fathers to the children, and the heart of the children to their fathers" (Mal. 4:5-6).

The appearance of Elijah to the Prophet Joseph Smith and Oliver Cowdery in the Kirtland Temple in 1836 inaugurated anew this spirit (D&C 110:13). The spirit of Elijah is active in the impetus anyone feels toward finding and cherishing family members and family ties past and present. In the global sense, the spirit of Elijah is the spirit of love that may eventually overcome all human family estrangements. Then the priesthood power can bind generations together in eternal family relationships and "seal the children to the fathers and fathers to the children" within the gospel of Jesus Christ (WJS, p. 329).

Elijah and Keys of Priesthood Authority – Elder Russell M Nelson

https://www.lds.org/general-conference/1994/10/the-spirit-of-elijah?lang=eng 

In 1844, Joseph Smith asked, “What is this office and work of Elijah?” The Prophet promptly answered his own question: “It is one of the greatest and most important subjects that God has revealed. …

“This is the spirit of Elijah, that we redeem our dead, and connect ourselves with our fathers which are in heaven. … This is the power of Elijah and the keys of the kingdom of Jehovah.”27

Some among us still have neither perceived the Spirit of Elijah nor its power. Yet, we are bound by this warning:

“These are principles in relation to the dead and the living that cannot be lightly passed over. … For their salvation is necessary and essential to our salvation … they without us cannot be made perfect—neither can we without our dead be made perfect.”28

Joseph Smith’s responsibility was to “lay the foundation”29 for this great work. Important details were to be revealed later. At April conference 1894, President Wilford Woodruff announced this revelation: “We want the Latter-day Saints from this time to trace their genealogies as far as they can, and to be sealed to their fathers and mothers. Have children sealed to their parents, and run this chain through as far as you can get it. … This is the will of the Lord to his people.”30

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