Hebrews 10:5 Consequently, when Christ came into the world, he said, “Sacrifices and offerings you have not desired, but a body have you prepared for me;”
In readings by those who believe that Jesus already existed in heaven (Trinity, Jehovah’s Witnesses) this is often taken to mean that God prepared a foetus in Mary’s womb and had Jesus descend into it. Which would contradict verses such as Luke 2:40, 2:52 which describe Jesus growing and learning as a normal baby, as well as the statements of the New Testament that Jesus was “conceived” son of Mary, and descended from David, Abraham, Adam.
But in fact “a body you have prepared for me” is just a Jewish idiom for the preparation of a slave in the Old Testament who commits himself to be a servant for life to a particular master.
Exodus 21:5 But if the slave plainly says, ‘I love my master, my wife, and my children; I will not go out free,’ 6 then his master shall bring him to God, and he shall bring him to the door or the doorpost. And his master shall pierce his ear with a needle, and he shall be his slave forever.
Psalm 40:6 (Hebrew) In sacrifice and offering you have not delighted,
but my ears you have pierced.
Burnt offering and sin offering
you have not required.Psalm 40:6 (Greek OT) In sacrifice and offering you have not delighted,
but a body you have prepared for me.
Burnt offering and sin offering
you have not required.
Why should “my ears you have pierced” in Hebrew be translated “a body you have prepared for me” in Greek? Because when the Old Testament was translated into Greek in the 3rd-2nd Century before Christ, neither the Jews in Greek-speaking cities like Alexandria, nor those “God-fearing” Greeks who took up elements of the Jewish religion without being circumcised, practised any more the piercing of slaves’ ears with this meaning. Also possibly that the translators of the Greek OT thought that the image of King David having his ear pierced as a slave in this way was demeaning (although it is David’s own image). Therefore “a body you have prepared me” was used to paraphrase the rite in Exodus in a way Greek speaking Jews and Greeks would understand better. In this way it entered the language and found its way into Hebrews 10:5.
Additionally looking at the context of Hebrews 10:5 it becomes clear that the body prepared for Jesus is prepared for sacrifice on the cross. And like Exodus where the nailing of the slave’s ear to the wooden doorpost is the act of an adult, not connected with the slave’s birth, so Christ’s preparation for the nailing of his body to the cross is the act of an adult, not connected with Christ’s birth.
5 Consequently, when Christ came into the world, he said,
“Sacrifices and offerings you have not desired,
but a body have you prepared for me;
6 in burnt offerings and sin offerings
you have taken no pleasure.
7 Then I said, ‘Behold, I have come to do your will, O God,
as it is written of me in the scroll of the book.’”8 When he said above, “You have neither desired nor taken pleasure in sacrifices and offerings and burnt offerings and sin offerings” (these are offered according to the law), 9 then he added, “Behold, I have come to do your will.” He does away with the first in order to establish the second. 10 And by that will we have been sanctified through the offering of the body of Jesus Christ once for all.
Christ “coming into the world” of course includes his birth as well (see Gal. 4:4. 2Co.5:21 etc.) but it is also adult Jesus coming into the world of the Jews. The writer of Hebrews’ own explanation “through the offering of the body of Jesus Christ” is that this passage “but a body have you prepared for me;” is about the offering of the body of the adult Jesus, for whom his whole life, not just his birth, was a preparation