“It was especially the work of God the Father to prepare Christ a body, as appears by Heb. 10:5.” Since it was impossible for the blood of bulls and goats to take away sin, Hebrews 10:1-10 points out the need for the Divine Son of God to be sacrificed for sin. This is why Jesus came into the world (Heb. 10:5). The phrase “coming into the world” (Heb. 10:5) is used to highlight Jesus’ preincarnate eternal existence and his subsequent incarnation whereby full humanity and full divinity were joined in the one person of Jesus.
The writer of Hebrews quoted Psalm 40:6-8 to highlight the ineffectiveness of purely physical sacrifices and the need for the sacrifice of the God-Man Jesus. The quotation of Psalm 40:6-8 is attributed to a dialogue between the Father and Son. Other Psalms are treated this way in the book of Hebrews (Heb. 1:6; 2:12-13; 10:5-7). So, Jesus is presented as saying to the Father, “you did not desire sacrifice and offering, but you prepared a body for me.” The physical sacrifices prescribed in the Old Testament were not able to take away sin (Heb. 10:4). Therefore, the divine Word added full human nature to his person to make the perfect atoning sacrifice. As Anselm said in his work Why God Became Man, the debt of sin is that “which no one can pay except God, and no one ought to pay except man: it is necessary that a God-Man should pay it.”
“O Thou the Eternal Son of God” (William Dix, 1864)
O Thou th’Eternal Son of God, The Lamb for sinners slain, we worship while Thy head is bowed in agony and pain. None tread with Thee the holy place; Thou sufferest alone; Thine is the perfect sacrifice which only can atone.
 Jonathan Edwards, The Miscellanies: (Entry Nos. 833–1152), ed. Harry S. Stout, Amy Plantinga Pauw, and Perry Miller, vol. 20, The Works of Jonathan Edwards (New Haven; London: Yale University Press, 2002), 235.
 John used the phrase in John 1:9; 6:14; 9:39; 12:46; 16:28; and 18:37.
 Anselm, Why God Became Man. Anselm of Canterbury: The Major Works. (Oxford: Oxford University Press, 1998), 320.