According to the book of Hebrews, Jesus is a high priest on the order of Melchizedek. In Genesis, Abraham met and paid tithes to Melchizedek. I understand there is controversy about who Melchizedek is. The David Jeremiah Study Bible asserts Melchizedek was not a pre-incarnation of Christ. I agree; Hebrews says M. was "made like the Son of God." Taking that literally, it means M. was created ("made") and had some characteristics similar to the Son of God. Hebrews says M. was without genealogy, without a mother or father, and without beginning of days. "Without beginning of days" makes it sound like he always existed, like Christ. But that could mean there was no day on earth in which he first came into existence. The same is true of the angels. They were created before the earth was. But M. is not an angel, otherwise the Bible would just call him an angel like it calls Michael and Gabriel angels. I have a theory/proposal that Melchizedek is in his own class of beings, neither angel nor human. (He took on human characteristics, like angels sometimes have, and Christ also left heaven to become human.) God, no, created, yes, but of his own type of being. There may or may not be other beings in his class of beings. Who knows, he may even be more powerful than Satan.
Actually, the Greek says Melche Zedek/ King of Righteousness was a facsimile of the Son of God; for the purposes of typing the Son of God, he was not named in the passage, but the ancient texts plainly state he was Shem, who was serving in the office of high priest and high king over earth, for God.
That is an office that Adam had, lost, and would have had forever over earth if he had not fallen, and sold earth into the powers of the satans.
FYI: Shem outlived Abraham, and Abraham lived with Shem and Noah from age 10 to age 39, when the Tower of Babel fell.
Noah died when Abraham was 58, but Shem outlived him.
The office of firstborn of earth is that of high priest and high king and was held by the patriarchs who could not live forever, because of the fall.
It went from Adam to Cain, who killed his brother and lost it, then to Seth, and down to Methusaleh, Noah, Shem, and then to Abraham.
And it was the blessing Shem gave Abraham, after he routed Nimrod (Amraphael) and the kings in Genesis 14.
The office was given to the tribe of Levi, and Moses had it, then Moses gave the office of high priest to Aaron, but not the office of high king.
The Office of high king went to David of the tribe of Judah.
John the Baptist, cousin to Jesus/Yeshua, baptized Jesus back into the office of high priest, and by right of being the Firstborn Son of God since the first, firstborn son Adam, died, Jesus has redeemed the sold into sin and corruption earth back and will take possession of it when He takes that power unto Himself, as seen in Revelation.
He is High Priest and High King, and will serve earth forever in that office as the never dying Father of the human being race who will never leave us orphans, spiritually, as our father Adam did.
Read the book of the Upright/Book of Jasher (the real one), for the history, but the Torah tells you why the office is held for the Messiah.