“The issue is not that we are taught by the advent of Christ to read the Scriptures retrospectively, but that the Christ in whom Christians place their trust and now worship is the same Christ who long ago revealed the ways of God in the Scriptures. The Venerable Bede, commenting on 1 Peter 1:12 early in the eighth century, put it this way:
He had said previously that the Spirit of Christ had foretold his sufferings and subsequent glories to the prophets, and now he says that the apostles are proclaiming the same things to them by the Holy Spirit sent from heaven.
Hence it is evident that the same spirit of Christ was formerly in the prophets as was afterwards in the apostles, and therefore each was preaching the same faith in the suffering and subsequent glory of Christ to the peoples, the (prophets) that it was still to come, the (apostles) that it had already come; and because of this (they preached) that there is one Church, part of which preceded the bodily coming of the Lord, part of which followed (it). Interpretively, then, Israel’s Scriptures testify to the Christ (and no other) who first inspired them.”
(Joel B. Green, Seized by Truth, pp 38-39)
The take-away is that the entire Bible – both the Old and New Testaments – bear witness to the same Lord Jesus Christ. It is the same Holy Spirit who inspires the authors of both covenants.
“You search the scriptures, because you think that in them you have eternal life; and it is they that bear witness to me . . . If you believed Moses, you would believe me, for he wrote of me.” (John 5:39, 46)