Why didn't the killing of Jesus stop God's program?
The killing of Jesus did not stop God’s program because God raised Him from the dead. Although Israel rejected and crucified their Messiah, He is still alive, and Peter made this known to Israel. Their message then was to repent of rejecting their Messiah.
Les explains that just because they killed Him, that didn’t stop God’s program, because God raised Him from the dead. He’s still alive, and Peter is making it known. Peter is addressing only the nation of Israel on the same ground as before the crucifixion, the Abrahamic covenant and the other various Old Testament covenants. He accuses Israel of having killed their Messiah, even though they did not do it with their own hands; they demanded it and caused Rome to carry it out. They had openly rejected their Messiah. Peter tells the whole house of Israel to know assuredly that God made this same Jesus, whom they crucified, Lord in Christ. The message to Israel was to repent of having rejected their Messiah, and to prove repentance with baptism.
Therefore let all the house of Israel know assuredly, that God hath made that same Jesus, whom ye have crucified, both Lord and Christ.