Why isn't the church age mentioned in Old Testament prophecy?
The church age is absent from Old Testament prophecy because the prophets knew nothing of a 1900-year period of grace. They saw Christ's crucifixion, resurrection, ascension, the wrath of God, and the Kingdom as consecutive events, so the interval of the church age was not revealed to them.
Les explains that he lists the crucifixion, resurrection, ascension, the nations going into derision, the wrath of God, and the Kingdom, then asks what he left out: the 1900 and some years of the church age. He asks why he left it out, and answers, 'Because the Old Testament does.' It is not packed there because the prophets did not know anything about a 1900-year period of grace; they just saw all these things coming down as it was prophesied. Peter, in Acts chapter 2, is in the same boat and the same mode of language Jesus used. He quotes Joel, an Old Testament prophet, saying 'this is that' which was spoken by Joel, quoting word by word about the last days and the Spirit being poured out. Joel wrote prophecy of a future day, and it happened at Pentecost. So the Old Testament prophets saw no gap for the church age.