The Messiah would do God's (His Father) will.
OT Prophecy NT Fulfillment
Psalm 40:7–8
[7] Then said I, Lo, I come: in the volume of the book it is written of me,
[8] I delight to do thy will, O my God: yea, thy law is within my heart.
John 5:30
"I can of mine own self do nothing: as I hear, I judge: and my judgment is just; because I seek not mine own will, but the will of the Father which hath sent me."
Tanakh – Ketuvim – Psalms 40:8–9
[8] Then said I: 'Lo, I am come with the roll of a book which is prescribed for me;
[9] I delight to do Thy will, O my G-d; yea, Thy law is in my inmost parts.
Hebrew OT – Psalms 40:8–9
[40:8] אָז אָמַרְתִּי הִנֵּה־בָאתִי
בִּמְגִלַּת־סֵפֶר כָּתוּב עָלָי
[40:9] לַעֲשׂוֹת רְצוֹנְךָ אֱלֹהַי חָפָצְתִּי
וְתוֹרָתְךָ בְּתוֹךְ מֵעָי