Charles H. Spurgeon on Psalms 40:7

The volume of the book. But what volume of manuscript roll is here meant? Plainly, the one which was already extant when the psalmist was writing. If the psalmist was David himself (as the title of the Psalm seems to affirm), the only parts of the Hebrew Scriptures then extant, and of course, the only part to which he could refer, must have been the Pentateuch, and perhaps the book of Joshua. Beyond any reasonable doubt, them, the kefalis biblion (rpo tlnm) was the Pentateuch...But I apprehend the meaning of the writer to be, that the book of the law, which prescribes sacrifices that were merely skiai or parabolai of the great atoning sacrifice by Christ, did itself teach, by the use of these, that something of a higher and better nature was to be looked for than Levitical rites. In a word, it pointed to the Messiah; or, some of the contents of the written law had respect to him. Moses Stuart, M.A., in "A Commentary on the Epistle to the Hebrews," 1851.