Why did the apostles in early Acts operate only on the Old Testament program?
The apostles operated only on the Old Testament program because God had revealed only that to them. The plan to turn to the Gentiles for an undetermined period remained a secret in God's mind. They had no concept of it, and it was not their fault.
Les explains that during the early chapters of Acts, Peter and the other eleven could only operate on what God had already revealed, which was the Old Testament program. Peter had no concept that God would turn to the Gentiles for 1900 and some years; none of the apostles did. It was not their fault, because God had been holding that purpose secret and was still giving Israel opportunity to repent of what they had done to their Messiah. Les notes that Peter in early Acts is not talking to the church or to Gentiles; he is addressing Israel. He also says the rapture and Church doctrine are not found in the Gospels or Old Testament because they were a secret in the mind of God, and God was dealing only with Israel. After Christ ascended and Israel continued rejecting the offer of the King and Kingdom, God moved that program into the future, inserted an undetermined period, after which the seven years will come, Christ will return, and the King will set up His Kingdom. This reinforces why the apostles operated on the Old Testament program: the Church truth had not yet been revealed.