The church age is a mystery unforeseen by the Old Testament Prophets.
To emphasize that I am not putting these words into the mouths of some of the most learned and respected classic dispensationalists, here are are some direct quotes:
"The first prediction relative to the true Church was uttered by Christ, being recorded in Matthew 16:18." 1
"The founding and success of the church during the Time of the Gentiles was a mystery, not explained until New Testament times." 2
"Dispensationalists have regarded the present age as a parenthesis unexpected and without specific prediction in the Old Testament." 3
"It has been illustrated how this whole age existed in the mind of God without having been revealed in the Old Testament." 4
"The church is a mystery, unrevealed in the Old Testament." 5
"The Church is a mystery in the sense that it was completely unrevealed in the Old Testament and now revealed in the New Testament." 6
Is that what the bible teaches? Well, no it is not. To quote just two passages:
And likewise, all the prophets who have spoken, from Samuel and his successors onward, also announced these days (Acts 3:24, NASB)
These words from Peter come after Pentecost, which is considered by dispensationalists as the beginning of the unforeseen church age. So Peter says that "these days", which are by the dispensationalists own definition in the unforeseen church age, were spoken of not by "no prophet" but by all the prophets.
Also, from the prophet Joel:
"And afterward, I will pour out my Spirit on all people. Your sons and daughters will prophesy, your old men will dream dreams, your young men will see visions. (Joel 2:28, NASB)
This prophesy was fulfilled at Pentecost, again the very day the church age is said to have begun.
1 L. S. Chafer, Systematic Theology, 8 vols. (Dallas: Dallas Seminary Press, 1947), 4:374.
2 J. F. Walvoord, Armageddon, Oil and the Middle East Crisis, p. 50.
3 J. F. Walvoord, Millennial Kingdom, p. 227)
4 J. Dwight Pentecost, Things to Come (Grand Rapids: Zondervan, 1958), p. 137.
5 Ibid., p. 193.
6 Ryrie, The Basis of the Premillennial Faith (Loizeaux Brothers, 1953), p. 136.