Final answer:
Moses, Elias, and Elijah appeared to Prophet Joseph Smith and Oliver Cowdery in the Kirtland Temple during the Kirtland Temple vision, restoring important priesthood keys.
Step-by-step explanation:
Moses, Elias, and Elijah appeared to the Prophet Joseph Smith and Oliver Cowdery in the Kirtland Temple as part of a significant event in Mormon history known as the Kirtland Temple vision.
This vision took place on April 3, 1836, and it is described in Doctrine and Covenants section 110. During this vision, Moses restored the keys of the gathering of Israel, Elias restored the keys of the dispensation of the gospel of Abraham, and Elijah restored the keys of sealing and the turning of the hearts of the fathers to their children.
These appearances were seen as a confirmation of the divine authority and the restoration of essential priesthood keys to Joseph Smith and Oliver Cowdery.