Joseph Smith - The Everlasting Priesthood

Throughout the scriptures, we are taught the "Plan of Salvation". Joseph Smith taught an essential part of that plan being the Melchizedek Priesthood -

“There has been a chain of authority and power from Adam down to the present time.”

Adam being a key figure in that chain of authority -

“The Priesthood was first given to Adam; he obtained the First Presidency, and held the keys of it from generation to generation. He obtained it in the Creation, before the world was formed, as in Gen. 1:26, 27, 28. He had dominion given him over every living creature. He is Michael the Archangel, spoken of in the Scriptures.... he was called of God to this office, and was the father of all living in his day, and to him was given the dominion. These men held keys first on earth, and then in heaven."

He stands at the head of all Melchizedek holders in the great plan -

“The Priesthood is an everlasting principle, and existed with God from eternity, and will to eternity, without beginning of days or end of years [see Joseph Smith Translation, Hebrews 7:3]. The keys have to be brought from heaven whenever the Gospel is sent. When they are revealed from heaven, it is by Adam’s authority."

Adam -

"...is the father of the human family, and presides over the spirits of all men, and all that have had the keys must stand before him in this grand council. … The Son of Man stands before him, and there is given him glory and dominion. Adam delivers up his stewardship to Christ, that which was delivered to him as holding the keys of the universe, but retains his standing as head of the human family.
“… The Father called all spirits before Him at the creation of man, and organized them. He (Adam) is the head, and was told to multiply. The keys were first given to him, and by him to others. He will have to give an account of his stewardship, and they to him."

The Prophet records -

“I saw Adam in the valley of Adam-ondi-Ahman. He called together his children and blessed them with a patriarchal blessing. The Lord appeared in their midst, and he (Adam) blessed them all, and foretold what should befall them to the latest generation.
This is why Adam blessed his posterity; he wanted to bring them into the presence of God..."

The plan cannot be completely taught without teaching the role of Adam -

“Adam … was the first man, who is spoken of in Daniel as being the ‘Ancient of Days’ [Daniel 7:9], or in other words, the first and oldest of all, the great, grand progenitor of whom it is said in another place he is Michael, because he was the first and father of all, not only by progeny, but the first to hold the spiritual blessings, to whom was made known the plan of ordinances for the salvation of his posterity unto the end, and to whom Christ was first revealed, and through whom Christ has been revealed from heaven, and will continue to be revealed from henceforth. Adam holds the keys of the dispensation of the fullness of times; i.e., the dispensation of all the times have been and will be revealed through him from the beginning to Christ, and from Christ to the end of all the dispensations that are to be revealed…"