Building a bit on the previous post about Messiah in the OT, I'd like to add a couple more seed-thoughts.
The relationship of Old and New Testaments is of course a massive topic, subject of thousands of pages by men vastly my superior. Yet I have a thought I'd like to contribute which I haven't seen elsewhere phrased exactly thus. Maybe for good reason. Let's see.
The relationship has been likened to form and fullness; to shadow and substance; to Law and Gospel; to type and antitype.
My suggestion: the relationship is that of "Huh?" to "Oh!"
Here's what I mean: in many forms and in many ways God spoke to the Fathers in the prophets. He meant every word He said. Every word had meaning for the original writers and audience, and that meaning was God's meaning.
At the same time, many of those meanings ultimately led to ambivalence, puzzlement, or even frustration. They led somewhere meaningful, yet incomplete. Followed out, thought through, they still would have to leave the serious and believing thinker trusting, yet baffled and unresolved. He's stuck at "Huh?"
But when the full-day revelation of the NT dawns, then and only then comes the "Oh!" of resolution and understanding.
We could single out a number of examples. I'll take two, and be brief about it.
God is One. We're clear on that, right? "Yahweh is our God, Yahweh is one" (Deuteronomy 6:4), the central confession of Israel's faith. "I am the LORD, and there is no other, besides me there is no God" (Isaiah 45:5a). Many Scriptures affirm this truth, beyond all doubt and ambiguity.
In fact, back to the verse asserting that Yahweh is "one." The word used there well accommodates the notion of a complex unity (cf. Genesis 2:24; Numbers 13:23), rather than a solitary unit (Genesis 22:2, 12, 16).
Then there's this figure, the Angel of Yahweh, who speaks both of and as Yahweh (Genesis 16:11 and 10, respectively) — that is, as if distinct from, and yet as if identical with, Yahweh. Scholars explain this language away as messenger-talk... but does that explanation really do justice to the language, and to the actions of those in His presence (cf. Joshua 5:13—6:5), and to the figure's appropriation of a title of the Messiah (Judges 13:18; Isaiah 9:6; virtually identical spelling in Hebrew)?
Add to these the baffling back and forths in Zechariah, where Yahweh speaks of Yahweh sending Him (e.g. 2:8-11 NAS). In fact, in Isaiah, Yahweh seems to send both Yahweh and His Spirit (48:16). Plus, Messiah will have God as His Father (Isaiah 7:14), and will bear His name (Isaiah 9:6; cf. Jeremiah 23:6).
So on the one hand, God is one. On the other, there's some kind of plurality going on there.
Suffering victim. Yet often in the psalms we see a very different picture. If we take David's experience as foreshadowing Messiah, we see him not only triumphing and reigning, but being mocked and forsaken and poured out in the dust of death (Psalm 22), and being abandoned by his friends (Psalm 41:9). Or laying aside types in favor of full-on predictive prophecy, we see the crystal-clear portrait of Messiah offering His soul as a sin offering, and dying (Isaiah 52:13 - 53:12). In fact, going back to the root-prophecy of Genesis 3:15, is not the Serpent-crushing Seed also stricken in His heel?
So, on the one hand, Messiah is a glorious, victorious Conqueror. And on the other, He suffers and dies, forsaken by God.
As to the first conundrum, we now see that there is but one God as to His essence, and that He is three as to His persons: Father, Son, and Spirit. All three appear and act in bold distinctness in the events and teaching surrounding the inauguration of the New Covenant, while confirming every jot of the teaching of the Old. So all of the OT is absolutely true, both in insisting at God's unity, and hinting at a plurality within that unity.
As I said, this is true in a wide variety of ways. Many mysteries are stirred and tales half-told, left unresolved and unsatisfied by the time Malachi (or 2 Chronicles, in the Hebrew Bible) is finally penned. But all those central mysteries are resolved with the complex of revelation unfolded in the coming of Christ.
The NT takes the OT's "Huh?" of penultimate bafflement, and transforms it into the "Oh!" of ultimate fulfillment.