Psalm 40:7
Then said I, Lo, I come: in the volume of the book it is written of me,
Then said I,.... As in the council and covenant of peace, when and where he declared his willingness to come into the world, and make satisfaction for the sins of his people; so when the fulness of time was come for his appearance in human nature he repeated the same; for of the time of his coming into the world are these words interpreted,
Hebrews 10:5; when sacrifice and offering God would not have any longer continued, and when a body was prepared him, then he said,
Lo, I come; O Father; as Apollinarius, in his metaphrase, adds; that is, freely, and without compulsion; immediately, at once, without any delay; and he himself, and not another; and this not by change of place, but by assumption of nature; taking the body, or human nature, prepared for him, and uniting it to himself; to which the word "lo" is prefixed as a note of attention and admiration; the incarnation of Christ being a wonderful affair, and of the utmost moment and importance;
in the volume of the book it is written of me; either in the book of divine predestination, in the purposes and decrees of God, Ps 139:16; or in the book of the Scriptures; either in general, John 5:39
Luke 24:27; or particularly in the book of the Psalms, Psalms 1:1; or rather in the book of the law, the five books of Moses, since these were the only books or volumes that were composed at the writing of this psalm; and it has respect not to Deuteronomy 18:15; nor Deuteronomy 17:18; nor Exodus 21:6; but rather Genesis 3:15; and seeing the coming of Christ into the world was not only appointed of God, agreed unto by Christ, but was prophesied of, and penned down in the sacred writings; therefore at the appointed time he came, freely and willingly. This book is called a volume, or roll, alluding to the manner of writing formerly; when what was written was finished, it was rolled about a stick in the manner of a cylinder; and in this form is the book of the law with the Jews to this day; See Gill on "Luke 4:17".