Ps 110 4 The LORD has sworn
and will not change his mind:
"You are a priest forever,
in the order of Melchizedek."

This Psalm is focusing on the eternal King who rules all nations by the pronouncements of the law, covenants, curses, statutes, decrees and promises. This king who is also a priest is not appointed in the succession of earthly priest. Because the Psalmist introduces Melchizedek as the priest with no beginning or ending, he is teaching that the eternal pronouncements are set apart from the words that are spoken by earthly kings and priest. The pronouncements are God speaking all things into existence from nothing. The law with its ceremonies had no authority to bring about the circumstances of the kingdom.

This King and Priest rules the nations through life and death. He is teaching Gods blessing and cursing that where pronounced from the temple on the mountain of Jerusalem are a metaphor for Gods control over the wills of all men. This Melchizedek rules the wills of men through pronouncements.

The Psalmist is teaching that Gods desires are expressed in the law, covenants etc. These eternal desires that determine the beginning of time to the end that are spoken in the law , covenants ,curses etc are revealed for David and the priest in order to create the justice and authority to rule all the nations. They are the sworn testimonies of God Most High who is the commander of the armies of Israel. So just as Gods law was set apart as the eternal law so to the entire earthly priesthood was acted upon by the eternal government of Melchizedek.Gen 14 18 Then Melchizedek king of Salem brought out bread and wine. He was priest of God Most High, 19 and he blessed Abram, saying,

"Blessed be Abram by God Most High,
Creator F69 of heaven and earth.
20 And blessed be God Most High,
who delivered your enemies into your hand."