psalms 40:6 Sacrifice and offering thou didst not desire; mine ears hast thou opened: burnt offering and sin offering hast thou not required. - Free Bible Online

      6-8. In Paul's view this passage has more meaning than the mere expression of grateful devotion to God's service. He represents Christ as declaring that the sacrifices, whether vegetable or animal, general or special expiatory offerings, would not avail to meet the demands of God's law, and that He had come to render the required satisfaction, which he states was effected by "the offering of the body of Christ" [Heb 10:10], for that is the "will of God" which Christ came to fulfil or do, in order to effect man's redemption. We thus see that the contrast to the unsatisfactory character assigned the Old Testament offerings in Ps 40:6 is found in the compliance with God's law (compare Ps 40:7, 8). Of course, as Paul and other New Testament writers explain Christ's work, it consisted in more than being made under the law or obeying its precepts. It required an "obedience unto death" [Php 2:8], and that is the compliance here chiefly intended, and which makes the contrast with Ps 40:6 clear.
      mine ears hast thou opened--Whether allusion is made to the custom of boring a servant's ear, in token of voluntary and perpetual enslavement (Ex 21:6), or that the opening of the ear, as in Isa 48:8; 50:5 (though by a different word in Hebrew) denotes obedience by the common figure of hearing for obeying, it is evident that the clause is designed to express a devotion to God's will as avowed more fully in Ps 40:8, and already explained. Paul, however, uses the words, "a body hast thou prepared me" [Heb 10:5], which are found in the Septuagint in the place of the words, "mine ears hast thou opened." He does not lay any stress on this clause, and his argument is complete without it. It is, perhaps, to be regarded rather as an interpretation or free translation by the Septuagint, than either an addition or attempt at verbal translation. The Septuagint translators may have had reference to Christ's vicarious sufferings as taught in other Scriptures, as in Isa 53:4-11; at all events, the sense is substantially the same, as a body was essential to the required obedience (compare Ro 7:4; 1Pe 2:24).

JFB.