He is in the book
In Hebrews 10:7, the verse is actually a quotation from the Old Testament, specifically Psalm 40:7. The verse in Hebrews 10:7 says, “Then I said, ‘Behold, I have come—in the volume of the book it is written of Me—to do Your will, O God.'”
The phrase “coming in the volume of the book” refers to the concept that the entire Old Testament scripture, particularly the prophecies and promises found within it, point forward to Jesus Christ. In this context, the “book” refers to the sacred writings of the Old Testament.
The verse is expressing the idea that Jesus came into the world to fulfill the will of God as foretold in the Old Testament scriptures. It emphasizes the continuity and fulfillment of God’s plan through Jesus Christ as the central figure in God’s redemptive work.
Therefore, the one who is coming in the volume of the book is Jesus Christ, fulfilling the prophecies and promises of the Old Testament and establishing the new covenant through His life, death, and resurrection.