Verse Text:
"The LORD has sworn and will not change His mind: 'You are a priest forever in the order of Melchizedek.'" (Berean Standard Bible)

Context and Background:
Psalm 110 is a royal psalm attributed to King David, and it is one of the most frequently quoted Old Testament passages in the New Testament. This psalm is considered a Messianic prophecy, pointing to the coming of a future king who would also serve as a priest. The verse in question, Psalm 110:4, is pivotal in understanding the dual role of the Messiah as both king and priest.

Theological Significance:
The declaration in Psalm 110:4 is unique in its combination of kingship and priesthood, roles that were traditionally separate in ancient Israel. The reference to the "order of Melchizedek" is significant because Melchizedek, who appears in Genesis 14:18-20, was both a king and a priest. This dual role prefigures the Messianic office of Jesus Christ, who is recognized in the New Testament as fulfilling both roles.

Melchizedek's Order:
Melchizedek, the king of Salem and priest of God Most High, is a mysterious figure who blesses Abram and receives tithes from him. His priesthood is not based on lineage or descent, unlike the Levitical priesthood, which is tied to the tribe of Levi. This makes Melchizedek's priesthood eternal and universal, qualities that are ascribed to the Messiah in Psalm 110:4.

New Testament Fulfillment:
The New Testament, particularly the Book of Hebrews, expounds on Psalm 110:4 to affirm Jesus Christ's eternal priesthood. Hebrews 5:6, 6:20, and 7:17 explicitly cite this verse to demonstrate that Jesus is the ultimate high priest, surpassing the Levitical priesthood. His priesthood is eternal, unchangeable, and based on the power of an indestructible life, as described in Hebrews 7:16.

Divine Oath:
The phrase "The LORD has sworn and will not change His mind" underscores the irrevocable nature of God's promise. This divine oath assures the permanence and certainty of the Messiah's priesthood. It emphasizes God's unchanging purpose and the reliability of His word, which is a cornerstone of faith for believers.

Messianic Expectation:
In Jewish tradition, the expectation of a Messiah who would embody both kingly and priestly functions is rooted in passages like Psalm 110:4. This expectation is fulfilled in the person of Jesus Christ, who, according to Christian belief, reigns as King and intercedes as High Priest.

Implications for Believers:
For Christians, Psalm 110:4 provides assurance of Christ's eternal intercession and sovereign rule. It affirms the belief in Jesus as the mediator between God and humanity, offering a perfect sacrifice for sin and continually advocating on behalf of believers. This verse encourages faith in the unchanging nature of God's promises and the ultimate victory of Christ's kingdom.