The Prophet Joseph Smith taught that the Priesthood was the channel through which the Lord would reveal his sacred truths. Thus, in the restoration of the gospel one of the first acts was to restore the Aaronic and Melchizedek Priesthoods. This established the channel on the earth through which the Lord could restore the many keys, truths, and principles to us, his children.
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The following is a powerful statement by the Prophet Joseph Smith about the heavenly priesthood uniting with the earthly to bring about the great purposes of God:
The building up of Zion is a cause that has interested the people of God in every age; it is a theme upon which prophets, priests and kings have dwelt with peculiar delight; they have looked forward with joyful anticipation to the day in which we live; and fired with heavenly and joyful anticipations they have sung and written and prophesied of this our day; but they died without the sight; we are the favored people that God has made choice of to bring about the Latter-day glory; it is left for us to see, participate in and help to roll forward the Latter-day glory, "the dispensation of the fulness of times, when God will gather together all things that are in heaven, and all things that are upon the earth," "even in one," when the Saints of God will be gathered in one from every nation, and kindred, and people, and tongue, when the Jews will be gathered together into one, the wicked will also be gathered together to be destroyed, as spoken of by the prophets; the Spirit of God will also dwell with His people, and be withdrawn from the rest of the nations, and all things whether in heaven or on earth will be in one, even in Christ. The heavenly Priesthood will unite with the earthly, to bring about those great purposes; and whilst we are thus united in one common cause, to roll forth the kingdom of God, the heavenly Priesthood are not idle spectators, the Spirit of God will be showered down from above, and it will dwell in our midst. The blessings of the Most High will rest upon our tabernacles, and our name will be handed down to future ages; our children will rise up and call us blessed; and generations yet unborn will dwell with peculiar delight upon the scenes that we have passed through, the privations that we have endured; the untiring zeal that we have manifested; the all but insurmountable difficulties that we have overcome in laying the foundation of a work that brought about the glory and blessing which they will realize; a work that God and angels have contemplated with delight for generations past; that fired the souls of the ancient patriarchs and prophets; a work that is destined to bring about the destruction of the powers of darkness, the renovation of the earth, the glory of God, and the salvation of the human family. (May 2, 1842.) (emphasis added)
(Joseph Smith, Teachings of the Prophet Joseph Smith, selected and arranged by Joseph Fielding Smith, p.231)