Hebrews 10:7

7.In the volume or chapter of the book, etc. Volume is properly the meaning of the Hebrew word; for we know that books were formerly rolled up in the form of a cylinder. There is also nothing unreasonable in understanding book as meaning the Law, which prescribes to all God’s children the rule of a holy life; though it seems to me a more suitable view to consider him as saying, that he deemed himself to be in the catalogue of those who render themselves obedient to God. The Law, indeed, bids us all to obey God; but David means, that he was numbered among those who are called to obey God; and then he testifies that he obeyed his vocation, by adding, I come to do thy will; and this peculiarly belongs to Christ. For though all the saints aspire after the righteousness of God, yet it is Christ alone who was fully competent to do God’s will.

This passage, however, ought to stimulate us all to render prompt obedience to God; for Christ is a pattern of perfect obedience for this end, that all who are his may contend with one another in imitating him, that they may together respond to the call of God, and that their life may exemplify this saying, Lo, I come. To the same purpose is what follows, It is written, that is, that we should do the will of God, according to what is said elsewhere, that the end of our election is, to be holy and unblamable in his sight. (Colossians 1:22.)