Hebrews 10:5 refers to what the Lord said at His incarnation. He said: “Sacrifice and offering thou wouldest not, but a body hast thou prepared me.” I understand from a footnote in my Bible that Hebrews 10:5 is a quotation from the LXX translation of Psalm 40:6. But the KJV of Psalm 40:6 does not say “a body hast thou prepared me.” It says “mine ears hast thou opened.” Calvin suggests that the Apostle was not scrupulous in the quotation. Wouldn’t this mean that he (the Apostle) allowed an error into the inspired letter?

First, you are right with regard to Hebrews 10:5 and Psalm 40:6. The Greek text (TR) of Hebrews 10:5 uses the [Greek] word sôma, which is rightly rendered “body,” whereas the Hebrew text of Psalm 40:6 uses the [Hebrew] word ozen, which is rightly rendered “ears.” It is commonly thought that the writer of Hebrews quoted from the Septuagint, of which there are indeed manuscripts that use sôma (body) for ozen (ear) at Psalm 40:6. Calvin, together with most commentators, believe that the “the Apostle followed the Greek translators when he said, ‘A body hast thou prepared’” (comm. on Hebrew 10:5). Having thus surmised, Calvin adds:

In quoting these words the Apostles were not so scrupulous, provided they perverted not Scripture to their own purpose. We must always have a regard to the end for which they quote passages, for they are very careful as to the main object, so as not to turn Scripture to another meaning; but as to words and other things, which bear not on the subject in hand, they use great freedom (ibid.).

What Calvin is essentially saying is that Apostle knew his Hebrew, and he was aware of the difference in the LXX rendering of the verse, but used it anyway because it does not change the meaning substantially. In order to have His ears opened or bored, Christ must first have a body, and since a body is a synecdoche (a figure of speech in which a whole is given for a part and vice versa) of a ear, it is not wrong for the LXX to render ozen (ear) with sôma (body). The LXX is not an inspired translation. However, since the Apostle was writing under inspiration, the portions quoted would then carry the apostolic stamp of inerrancy. This being the case, it would not be right to charge the Apostle for introducing errors into the inspired letter.

It may be questioned, however, how the translators of the LXX decided to translate “ear” with a synecdoche in the first place! Some commentators suggest that perhaps they understood the mystery contained in Psalm 40:6, that it refers to the incarnation; others suggest they were aided in the translation by the Holy Spirit and yet others suggest it was by providential coincidence. These opinions, however, are not entirely satisfactory (at least to me), for whichever opinion we choose, we may err by suggesting that the Apostles used and sanctioned an unreliable translation, or we may err by suggesting that the LXX is in some ways inspired.

Personally, I think that Dr. John Owen’s opinion deserves a little more consideration. Owen believed that the rendering of ozensôma (body) was not in fact done by the LXX translators, but by the Apostle under inspiration. The Apostle could of course do so as he was not bound to quote the Hebrew text verbatim nor to translate it word for word,—just as preachers, when offering proofs from the Bible do not necessarily quote word for word, but often paraphrase or quote in such a way as to fit the flow and context of the subject being dealt with, without compromising the original meaning of the quotation. Note the difference between the earlier suggestion that the LXX translators were responsible for the sôma (body) as compared to Owen’s suggestion that the Apostle was responsible. In the former, the quality of the LXX translation (it being a translation) would be compromised. In the latter, the Apostle is writing under inspiration for the instruction of the Church, and so it is proper for him to render as he did (“body” being suitably used as a synecdoche of “ear” to emphasise the point that a body is necessary in order for the Lord to do the will of the Father). (ear) with

But if we hold to this latter view, then how do we account for the fact that the LXX’s rendering of Psalm 40:6 is exactly as in Greek text of Hebrews 10:5? Owen asserts that it is so because “sundry passages have been unquestionably taken out of the New Testament, and inserted into that translation” (see Hebrews, 6.458). This is not at all unlikely given that the LXX OT continued to be copied and used in some parts of the church after the New Testament were written. Owen proves his point by showing that some old copies of the LXX actually have [the Greek] ôtia (ears) at Psalm 40:6 rather than sôma (body), and the Latin Vulgate had followed these early copies. Indeed, my own copy of the LXX, which was a scholarly edition put together by Alfred Rahlfs (Septuaginta, [Deutsche Bibelgesellschaft Stuttgart, 1979]), has ôtia (ears) at Psalm 40:6 rather than sôma
(body). Is it not likely that Owen is right?