Tim Keller nails is it in this video.
“You search the Scriptures because you think that in them you have eternal life; and it is they that bear witness about me” (John 5:39 ESV).
“And beginning with Moses and all the Prophets, he interpreted to them in all the Scriptures the things concerning himself.” (Luke 24:27 ESV)
And here’s a sermon series I did at Redeemer Church called, Gospel Witness: The Unfolding Glory of Jesus in the Old Testament. 20+ sermons looking at how the stories in the Old Testament are, ultimately, preaching the glory of Christ in the gospel. It’s all about Jesus.