For verily this generation shall not all pass away until an house shall be built unto the Lord, and a cloud shall rest upon it, which cloud shall be even the glory of the Lord, which shall fill the house.
And the sons of Moses, according to the Holy Priesthood which he received under the hand of his father-in-law, Jethro;
And Jethro received it under the hand of Caleb;
And Caleb received it under the hand of Elihu;
And Elihu under the hand of Jeremy;
And Jeremy under the hand of Gad;
And Gad under the hand of Esaias;
And Esaias received it under the hand of God.
Esaias also lived in the days of Abraham, and was blessed of him—
Which Abraham received the priesthood from Melchizedek, who received it through the lineage of his fathers, even till Noah;
(Doctrine & Covenants 84:6-14)
Firstly, I like this scripture because it's like reading a family pedigree chart. Or a line of authority card, which shows you that the line of priesthood power is unbroken.
Secondly, we learn that the prophet Abraham was ordained to the priesthood by the great High Priest Melchizedek, whom he served under.
This may be slightly off topic, but .. meh. It's in the book of Genesis.
And it's been on my mind lately ..
This scripture also confirms something .. and this is key. The priesthood - God's power - is ETERNAL. By that I mean, it has no beginning or end. It is everlasting. And it is powerful!
When Adam was lovingly kicked out of the Garden of Eden, God didn't abandon him. On the contrary. Our loving Heavenly Father taught his son Adam the principles of the gospel, including the plan of salvation. And the priesthood was conferred on him.
In fact, "he holds the keys of all the dispensations, which appointment he received under Jesus Christ".
“Adam received the holy priesthood and was commanded by the Lord to teach his children the principles of the gospel. Moreover, Adam was baptised for the remission of his sins, for the same principles by which men are saved now were the principles by which men were saved in the beginning.”
“As time went on men departed from the truth, and the priesthood was withdrawn. All flesh became corrupt, and the Lord said: “The end of all flesh is come before me, for the earth is filled with violence” (see Moses 8:13-30). So the flood was sent and the earth was cleansed from its wickedness. The Lord then appointed Noah and his sons to stand at the head of the human family. Noah, too, received the holy priesthood and taught his children the gospel.”“However, after a few hundred years had passed men became corrupt and refused to follow the teachings of their fathers. Again there was an apostasy. During this time there was on man in the city of Ur, among the few that remained faithful to the lord, who sought after righteousness. ..The Lord answered Abraham’s prayer, and he received the priesthood …” 
How about this one:
Do you know why we now call this priesthood after Melchizedek?
Look to Doctrine & Covenants 107:1-4 to find out:
There are, in the church, two priesthoods, namely, the Melchizedek and Aaronic, including the Levitical Priesthood.
Why the first is called the Melchizedek Priesthood is because Melchizedek was such a great high priest.
Before his day it was called the Holy Priesthood, after the Order of the Son of God.
But out of respect or reverence to the name of the Supreme Being, to avoid the too frequent repetition of his name, they, the church, in ancient days, called that priesthood after Melchizedek, or the Melchizedek Priesthood.
The prophet Joseph Smith taught:
“Every man who has a calling to minister to the inhabitants of the world was ordained to that very purpose in the grand council of heaven before this world was."
Abraham was present in this council, and was privileged to see the hosts of pre-existent spirits in a vision here.
So were you. Many noble and great ones. (read that in Abraham 3:22-23)
Just like Abraham, "thou art one of them, thou wast chosen before thou wast born."
Hold that thought for a moment, and look to Alma 13:3.
“All those who receive the Melchizedek Priesthood in this life were, as Alma teaches, “called and prepared from the foundation of the world according to the foreknowledge of God”, because they were among the noble and great in that premortal sphere.” 
Are you aware of the blessings of the Melchizedek Priesthood? But are you really?
“There are no blessings reserved for apostles that are not freely available to all the elders of the kingdom; blessings come because of obedience and personal righteousness, not because of administrative positions.” 
Here is a mighty table of the ten big potential blessings:
This is completely the work of Bruce R. McConkie . I just summarised it and table-ised it.
Go ahead and study this up. I don't blog that often, so you've got time.
And always consider: how did Abraham and Melchizedek act to obtain the priesthood AND these blessings?
How then must I act?
 Joseph Fielding Smith, Doctrines of Salvation, p.327-28
 Bruce R. McConkie, “God Foreordains His Prophets and His People”, Ensign, May 1974
 Bruce R. McConkie, “The Ten Blessings of the Priesthood”, Ensign, Nov.1977