After Isaiah 31, 32 continues with:
melek malak tsedeq sar sarar mishpat . [The] King will reign in righteousness and sar [rulers/ prince/s] will rule with [His lawful] judgment.
The "order/manner" of "king of righteousness [Melchi -Zedek] does not begin with the Messiah's Anointing to that office of firstborn of earth, as the wording shows. Tracing the beginning of it back, in the word of God, we see that it began with Adam, who fell and died as a son of God [Psalm 82, in the Hebrew only, when that one sar, Adam, the son of God, an "el", died], but received the sure promise of the "Seed of the Woman" who would restore all things by His Atonement, and reign over the dominion created for him as the holy Son of God, governing over it for the purpose it was created for, after He restores it for that holy purpose.
At the baptism of Jesus the Christ come in flesh, into the "order" of Melchi-Zedek , as "King of Peace" =the Priest of that Peace with God"; when He came up out of the waters the Holy Spirit of Peace descended upon Him, Anointing Him into office of High Priest of earth.
When He rose from the dead, after performing the prophesied and ordained "final Acceptable Offering of our Peace with God", He ascended on High and is seated on the Throne of Glory, as the Son of Man in heaven [in Eden, in fact], on that throne made for the Son of Man, from the beginning, to rule the dominion given to Adam.
He hasn't yet taken His great power over the ransomed kingdom unto Himself, though, and cast down all principalities and powers and wicked rulers in the heavenlies, and established His adopted sons in their positions of authority there, as "kings and priests: forever, in His New Man name -that's coming, and He is the King of Righteousness who will do what no "ish" [Isaiah 59, English "man"] born of Adam has ever or could ever do -because of the irrevocable defilement.
Melchi -Zedek is a title, passed as the blessing of "firstborn" from Adam down to Jesus Christ through the line of Seth, and Shem, third born son of Noah, got the blessing and held it until he passed it to Abraham, who passed it to .......and so on.
No one born in Adam could keep or even perform the duties of the office they held title to, in temporary succession, until He should come who would be the Everlasting Father and the King of Righteousness, whose princes rule in justice.
That theme is Genesis to Revelation, and if you would study to prove all things for yourself instead of insisting you have all knowledge of the Word of God and the doctrines of it as to the theme of Salvation for this earth and for the sons of Adam accomplished once, in the fulness of time for all , by the Kinsman/Redeemer; who Himself is YHWH in the second Person come in second Man creation flesh to be that Kinsman/Redeemer, and who is the "elected Firstborn" of earth, and who is the Anointed High Priest of earth in the line from Adam, through Seth -and so on- who ever lives to make intersession before the Glory above, for His own adopted sons;
and who is to be crowned the King of Kings who will rule in Righteousness and hold office of Priest and King, forever, as Adam was created to do in his dominion, from Eden above, before the fall, then you might begin to walk in the light of understanding of God's one plan for this created earth and its heavenly realm, which Adam was cast down from when he died as a son of God, and which the Kinsman/Redeemer, as Second Man, has shed His blood to atone for and will take His great power unto Himself and rule in Righteousness over His kingdom redeemed, from the Throne of Glory which no Adam ever ascended to, and was meant to be set upon, in Eden above.