Verse 7. Then said I. I the Messiah. Paul applies this directly to Christ, showing that he regarded the passage in the Psalm as referring to him as the speaker. Lo, I come. Come into the world, Heb 10:6. It is not easy to see how this could be applied to David in any circumstance of his life. There was no situation in which he could say that, since sacrifices and offerings were not what was demanded, he came to do the will of God in the place or stead of them. The time here referred to by the word "then" is, when it was manifest that sacrifices and offerings for sin would not answer all the purposes desirable, or when in view of that fact the purpose of the Redeemer is conceived as formed to enter upon a work which would effect what they could not.

In the volume of the book it is written of me. The word here rendered "volume" -- kefaliv -- means, properly, a little head; and then a knob, and here refers, doubtless, to the head or knob of the rod on which the Hebrew manuscripts were rolled. Books were usually so written as to be rolled up; and when they were read they were unrolled at one end of the manuscript, and rolled up at the other as fast as they were read. See Barnes "Lu 4:17".

The rods on which they were rolled had small heads, either for the purpose of holding them or for ornament; and hence the name head came metaphorically to be given to the roll or volume. But what volume is here intended? And where is that written which is here referred to if David was the author of the Psalm from which this is quoted, (Ps 40) then the book or volume which was then in existence must have been principally, if not entirely, the five books of Moses, and perhaps the books of Job, Joshua, and Judges, with probably a few of the Psalms. It is most natural to understand this of the Pentateuch, or the five books of Moses, as the word "volume," at that time, would undoubtedly have most naturally suggested that. But plainly, this could not refer to David himself, for in what part of the law of Moses, or in any of the volumes then extant, can a reference of this kind be found to David? There is no promise, no intimation that he would come "to do the will of God" with a view to effect that which could not be done by the sacrifices prescribed by the Jewish law. The reference of the language, therefore, must be to the Messiah -- to some place where it is represented that he would come to effect by his obedience what could not be done by the sacrifices and offerings under the law. But still, in the books of Moses, this language is not literally found, and the meaning must be, that this was the language which was there implied respecting the Messiah; or this was the substance of the description given of him, that he would come to take the place of those sacrifices, and by his obedience unto death would accomplish what they could not do. They had a reference to him; and it was contemplated, in their appointment, that their inefficiency would be such that there should be felt a necessity for a higher sacrifice, and when he should come they would all be done away. The whole language of the institution of sacrifices, and of the Mosaic economy, was, that a Saviour would hereafter come to do the will of God in making an atonement for the sin of the world. That there are places in the books of Moses which refer to the Saviour is expressly affirmed by Christ himself, (Joh 5:46) 46,) and by the apostles, (comp. Ac 26:23,) and that the general spirit of the institutions of Moses had reference to him is abundantly demonstrated in this epistle. The meaning here is, "I come to do thy will in making an atonement, for no other offering would expiate sin. That I would do this is the language of the Scriptures which predict my coming, and of the whole spirit and design of the ancient dispensation"

To do thy will, God. This expresses the amount of all that the Redeemer came to do. He came to do the will of God

(1) by perfect obedience to his law, and

(2) by making an atonement for sin -- becoming "obedient unto death," Php 2:8. The latter is the principal thought here, for the apostle is showing that sacrifice and offering such as were made under the law would not put away sin, and that Christ came, in contradistinction from them, to make a sacrifice that would be efficacious. Everywhere in the Scriptures it is held out as being the "will of God" that such an atonement should be made. There was salvation in no other way, nor was it possible that the race should be saved unless the Redeemer drank that cup of bitter sorrows. See Mt 26:39. We are not to suppose, however, that it was by mere arbitrary will that those sufferings were demanded. There were good reasons for all that the Saviour was to endure, though those reasons are not all made known to us.