Why are the rapture and Church doctrine not in the Old Testament?

Les explains that people should not look for the rapture or the Church in the Gospels, nor for the rapture of the Church, Church doctrine, or the Gospel as we know it in the Old Testament. It is not there because it was a secret held in the mind of God. In that program God was dealing only with the nation of Israel. After Christ ascended, Israel kept rejecting the offer of the King and the Kingdom, so God moved all this out into the future and put in an undetermined period of time. No one knows when it will end; then the seven years will come, then Christ will return, and then the King will come and set up His Kingdom. Les also notes that Peter and the other eleven operated only on what God had revealed, the Old Testament program. Peter had no concept of God turning to the Gentiles for 1900 and some years; none of them did, and it was not their fault. God had been holding it a secret and was giving Israel every opportunity to repent of what they had done to their Messiah. In the early chapters of Acts, Peter is not talking to the church or to Gentiles.