The Sealing Keys Restored

"Elijah was a courageous prophet who lived about seven hundred years before Jesus Christ. We know from modern-day revelation that Elijah was the last prophet to hold the sealing keys on earth before the Savior lived on the earth. Keys are rights of the holy priesthood to administer certain spiritual blessings or ordinances. The First Presidency and the Quorum of the Twelve Apostles hold all of the priesthood keys on earth, and those keys can be transferred only by the proper authority. Since Elijah was the last prophet to hold the sealing keys, he had the authority to restore them.
Malachi, another prophet of the Old Testament, prophesied that Elijah would come back to earth before the Second Coming. Even today, Jewish families leave an empty chair at the table during their Feast of the Passover to show that they are still waiting for his return.
Malachi’s prophecy came true when Elijah appeared in the Kirtland Temple. He restored the sealing keys to Joseph Smithand Oliver Cowdery on April 3, 1836 * —the second day of the Passover Feast, when many Jews throughout the world symbolically opened their doors to invite Elijah in.
Because Elijah restored the sealing keys, we can be sealed together as families throughout eternity. We show our gratitude for this sealing power by living worthy to enter the temple and by submitting our ancestors’ names to have temple ordinances done for them." - LDS.ORG