Psalms 110:4

Yahweh has made an affirmation in the most definite way possible and will not change His mind (cf. 2 Samuel 7:13; Psalms 89:3; Psalms 89:28-29; Psalms 89:34-35; Psalms 132:11). [Note: On the subject of God changing His mind, see Thomas L. Constable, "What Prayer Will and Will Not Change," in Essays in Honor of J. Dwight Pentecost, pp. 99-113; and Robert B. Chisholm Jr., "Does God ’Change His Mind’?" Bibliotheca Sacra 152:608 (October-December 1995):387-99.] Messiah will be a priest forever in the order of (i.e., after the manner of) Melchizedek (lit. king of righteousness). [Note: See M. J. Paul, "The Order of Melchizedek [Psalms 110:4 and Hebrews 7:3]," Westminster Theological Journal 49 (1987):195-211.] This is the first reference in Scripture to this "order" of priests. Melchizedek ruled over Salem (lit. peace), the ancient name for Jerusalem, where David also ruled. Melchizedek was also a priest of the Most High God (Genesis 14:18; cf. Hebrews 7:1). Thus he was both a king and a priest. Messiah would also be a king and a priest. In this sense, Messiah was a priest in the "order" of Melchizedek. He continued the type of priesthood Melchizedek had, namely, a kingly or royal priesthood.

If Yahweh sets up Messiah as a priest "forever," the Aaronic order of priests must end as God’s appointed order (cf. Hebrews 5:6; Hebrews 6:20; Hebrews 7:17; Hebrews 7:21). As both the Priest and the sacrificial Lamb, Messiah offered Himself as a substitute sacrifice on the cross (cf. Hebrews 7:27-28; Hebrews 10:10). Jesus was not of Aaron’s line since He descended from the tribe of Judah (cf. Hebrews 7:11-18). He is the new eternal High Priest (cf. Hebrews 7:21-26; Hebrews 7:28), and He mediates the New Covenant that replaces the Old Mosaic Covenant (cf. Hebrews 8:13; Hebrews 9:15).