Paul explains the importance of Priesthood, but most importantly he explains the importance of proper authority in the Priesthood. Paul explains; “…no man taketh this honour unto himself, but he that is called of God, as was Aaron.” (Hebrews 5:4) In other words, no one can claim to take upon themselves the Authority of the Priesthood, except they be called of God, like Aaron was called.
How was Aaron called of God? In Deuteronomy we learn how the Authority was transferred from Moses to Joshua upon the death of Moses; “…Joshua… was full of the spirit of wisdom; for Moses had laid his hands upon him…” (Deuteronomy 34:9) In the same manner, Aaron received the Priesthood from someone who had been called of God, through temple ordinances (see Exodus 40).
Paul explains that Christ was also given the Priesthood from God, and He gave the Priesthood to His Apostles; “…also Christ glorified not himself to be made an high priest; but he that said unto him, Thou arty my Son, to day have I begotten thee. As he saith also in another place, Thou art a priest for ever after the order of Melchisadec.” (Hebrews 5:6)
In Matthew, Christ called His Apostles and gave them the priesthood power; “… he had called unto him his twelve disciples, he gave them power…” (Matthew 10:1) This power was given by the laying on of hands.
This same power and authority exists in The Church of Jesus Christ of Latter-day Saints, which was restored to the earth through Joseph Smith. In the Joseph Smith History it reads;
“We still continued the work of translation, when, in the ensuing month (May, 1829), we on a certain day went into the woods to pray and inquire of the Lord respecting baptism for the remission of sins, that we found mentioned in the translation of the plates. While we were thus employed, praying and calling upon the Lord, a messenger from heaven descended in a cloud of light, and having laid his hands upon us, he ordained us, saying: Upon you my fellow servants, in the name of Messiah, I confer the Priesthood of Aaron, which holds the keys of the ministering of angels, and of the gospel of repentance, and of baptism by immersion for the remission of sins; and this shall never be taken again from the earth until the sons of Levi do offer again an offering unto the Lord in righteousness. He said this Aaronic Priesthood had not the power of laying on hands for the gift of the Holy Ghost, but that this should be conferred on us hereafter [The Melchizadek Priesthood];” (Joseph Smith History 1:68-70)