The Messiah would be a Priest after the order of Melchisedec.
OT Prophecy NT Fulfillment
Psalm 110:4
"The LORD hath sworn, and will not repent, Thou art a priest for ever after the order of Melchizedek."
Hebrews 6:17–20
[17] Wherein God, willing more abundantly to shew unto the heirs of promise the immutability of his counsel, confirmed it by an oath:
[18] That by two immutable things, in which it was impossible for God to lie, we might have a strong consolation, who have fled for refuge to lay hold upon the hope set before us:
[19] Which hope we have as an anchor of the soul, both sure and stedfast, and which entereth into that within the veil;
[20] Whither the forerunner is for us entered, even Jesus, made an high priest for ever after the order of Melchisedec.
Tanakh – Ketuvim – Psalms 110:4
"HaShem hath sworn, and will not repent: 'Thou art a priest for ever after the manner of Melchizedek.'"
Hebrew OT – Psalms 110:4
[110:4] נִשְׁבַּע יְהוָה וְלֹא יִנָּחֵם
אַתָּה־כֹהֵן לְעוֹלָם
עַל־דִּבְרָתִי מַלְכִּי־צֶדֶק