Before the creation of the world, God created an identity for Himself that He would use to enter human history. The first mention of this identity was at the judgment for sin in the garden of Eden. God told the serpent that the seed of woman would overcome him. This “seed of woman” was the Messiah. God used many other names for Messiah besides Messiah itself: the seed of Abraham (Genesis 22:18), the Prophet (Deuteronomy 18:15), the Son of David (2 Sam 7:12-14), Immanuel (Isaiah 7:14), the Prince of Peace (Isaiah 9:6), the Branch (Jeremiah 33:15), the Breaker (Micah 2:13), and many more. Thus the identity of Messiah was revealed piece by piece throughout the ages until the time of Jesus.
By the time of Jesus, expectations for the Messiah were high. However, the specifics of expectation were all over the map. No one had been able to piece together all the various prophecies about Messiah into one cohesive picture. Most people were looking for an earthly king like David, only greater. There were many pieces of the Messianic jigsaw puzzle, though, that just didn’t fit their perceptions (e.g. “He was despised and forsake of men” in Isaiah 53:3).
Jesus never proclaimed Himself to be the Messiah during His earthly life (though He did not deny it at His trial). Only when He was raised from the dead did He give permission to His disciples to make the fact known. Only when He was raised from the dead and seated in heaven could the combined prophecies begin to make sense. For the remainder of that generation, the apostles proclaimed Jesus of Nazareth as the Messiah, using all the Old Testament prophecies of His coming to tell the story. This much the apostles told in past tense. There were aspects of the Messianic prophecies, however, that were still in future tense at that time: how Messiah would rule the whole world, how the kingdom of God fit into this rule, what judgment would be like, and so on.
As the apostolic age was drawing to a close, it had become apparent that Messiah was an even greater Personage than anyone seems to have foreseen. So great, that some explanation was going to be needed about how the Messiah and God would relate in the final order. That time was coming soon, so no one would have to wait long for the answer. The answer, when it came, was stunning beyond description.
Messiah was an identity that God had used to live as a man on the earth, with all the limitations of a man. Messiah was not a separate being from God. Messiah was not even a separate person of God, for God is one. Rather, Messiah was God.
God had created the identity of Messiah ahead of time so that He could live as a man without detection. His purposes would have been compromised had people realized He was God while He was still on earth. Only once He had returned to heaven, and the gospel had been preached in the whole world throughout that generation, was it time to reveal the secret He had kept to Himself all those ages: He did not send anyone to do His work – He came and did it Himself.
For more on this subject, see:
There Is No Trinity; There Is Christ
Posts to Date on the Trinity Versus Christ