The Holy Spirit also testifies to us about this. First He says:
15. The Holy Ghost also is a witness, etc. “Now testify to us does also the Holy Spirit;” such may be the rendering of the words. The δὲ is translated “And,” by Macknight, and “Morever,” by Stuart, but “Now” seems the most suitable. — Ed This testimony from Jeremiah is not adduced the second time without reason or superfluously.
Here the apostle raises up and exalts the Lord Jesus Christ, as high as he had laid the Levitical priesthood low. He recommends Christ to them as the true high priest, the true atoning sacrifice, the antitype of all the rest: and this he illustrates, I. From the purpose and promise of God concerning Christ, which are frequently recorded in the volume of the book of God, Heb 10:7.
Commenting on Hebrews 10:7-18
Wherefore the Holy Ghost also is a witness to us,.... In Jer 31:33. This preface to the following citation shows that the books of the Old Testament are of divine original and authority; that the penmen of them were inspired by the Holy Ghost; that he existed in the times of the Old Testament; that he is truly and properly God, the Lord, or Jehovah...