The English Annotations (1645; 1651; 1657): Hebrew, “mine ear hast thou opened”; or “digged open.” It is a proverbial manner of speech, whereby there is implied the qualifying or fitting a person to obedience in service, the ear, or opening of the ear, being an emblem or symbol, or a metaphorical sign of obedience. Now Saint Paul, following the translation of the Septuagint, and being directed by the Spirit of God, expounds this of God’s sanctifying and fitting a body unto Christ, wherein he was obedient even unto the shameful death of the cross. Annotations on Hebrews 10:5
Ronald K. Rittgers (editor) Reformation Commentary on Scripture: New Testament XIII; Hebrews, James IVP Academic; 136
“The English Annotations” is a compilation and condensation of Reformed theology. The passage from Hebrews in question is referring to a quote from the Psalms which is typically translated “a body have you prepared for me.” The “me” in the passage is Jesus. The Psalmist is apparently thinking of the Old Testament practice to piercing the ear of a slave, who did not want to be released from service during the Year of Jubilee, with an awl (Exodus 21:5-6; Deuteronomy 15:16-17). Thus the body was prepared for service.