The Messiah would be the Son of God.
OT Prophecy NT Fulfillment
Psalm 2:7a
"I will declare the decree: the LORD hath said unto me, Thou art my Son; this day have I begotten thee."
Luke 1:31–35
[31] And, behold, thou shalt conceive in thy womb, and bring forth a son, and shalt call his name Jesus.
[32] He shall be great, and shall be called the Son of the Highest: and the Lord God shall give unto him the throne of his father David:
[33] And he shall reign over the house of Jacob for ever; and of his kingdom there shall be no end.
[34] Then said Mary unto the angel, How shall this be, seeing I know not a man?
[35] And the angel answered and said unto her, The Holy Ghost shall come upon thee, and the power of the Highest shall overshadow thee: therefore also that holy thing which shall be born of thee shall be called the Son of God.

Matthew 3:16–17
[16] And Jesus, when he was baptized, went up straightway out of the water: and, lo, the heavens were opened unto him, and he saw the Spirit of God descending like a dove, and lighting upon him:
[17] And lo a voice from heaven, saying, This is my beloved Son, in whom I am well pleased.

Hebrews 1:5–6
[5] For unto which of the angels said he at any time, Thou art my Son, this day have I begotten thee? And again, I will be to him a Father, and he shall be to me a Son?
[6] And again, when he bringeth in the firstbegotten into the world, he saith, And let all the angels of God worship him.
Tanakh – Ketuvim – Psalms 2:7a
"I will tell of the decree: HaShem said unto me: Thou art My son, this day have I begotten thee."
Hebrew OT – Psalms 2:7a
[2:7] אֲסַפְּרָה אֶל־חֹק
יְהוָה אָמַר אֵלַי
בְּנִי אַתָּה
אֲנִי הַיּוֹם יְלִדְתִּיךָ