I imagine that many Catholics, when they open the Old Testament and read the Books of Moses and the prophetic words of Isaiah, Jeremiah, and the like, expect them to be line after line of detailed description of what they were to expect of the Messiah: height, weight, shoe size, preferred method of dispatching Israel's enemies (that's what many expected his main occupation to be). They may be surprised, as I was, to find huge swaths of material that don't seem to refer to the Messiah at all. I mean, yeah, we get Isaiah 6 (the virgin shall conceive) and Wisdom 2 (the innocent man betrayed and murdered) and Exodus 34 (Moses' promise of a future prophet like himself), but what about all that other stuff? Israel's conquest of Canaan, their exile in Babylon, their fights against the Persians; all those words calling Israel to repentance so that God will restore them to the land? There's an awful lot of politics and battle statistics. And the psalms have some lovely bits of praise, and some rather depressing stuff, too, but not much in the way of presaging or predicting. What's it all got to do with Jesus dying and rising for our sins?
Christians learned to read their Scriptures in a new light, the Light of the World. Words and events were seen to have new meaning when viewed through the new lens of Jesus' Passion, Death, and Resurrection. Jesus himself began to make such connections for his disciples: "Just as Moses lifted up the serpent in the desert, so must the Son of Man be lifted up" (John 3:14). This story of the ancient Israelites in retrospect can be seen to prefigure the death of Christ. The apostles continued this line of figurative interpretation, as when St. Peter wrote that as Noah was saved through water in the ark, so baptism now saves us (1 Peter 3:20-21). All of these events are no longer just Israel's history; they are part of the great drama of salvation history.
The Church Fathers and other early Christian writers continued to find such connections. Origen saw in the binding of Isaac in Genesis 22 a figure of God sacrificing his own Son (when it could most truly be said that God provided the sacrifice). St. Gregory of Nyssa wrote an entire book tying every detail of the life of Moses to the mystery of Christ. Many of the Fathers, such as St. Hilary of Poitiers, saw Christ as the true speaker of the psalms, the ultimate heir of the promises to David. Examples abound, but all is summed up in St. Augustine's wonderful phrase: "The new is hidden in the old, the old revealed in the new."
Every letter of the Bible communicates something of Christ, for the Bible communicates the Word of God, who is Christ. All that was hidden is revealed in Christ. He is the light that enlightens everyone, and the darkness has not overcome it.