What did Peter and the apostles call on Israel to repent of?
Peter and the apostles called Israel to repent of the worst sin the nation had ever committed—killing their Messiah. Peter charged them directly: “You killed Him. You murdered Him.” That rejection of the Messiah was the sin from which Israel was urged to turn.
Les explains that Acts is a transitional book. At the beginning, Peter and the eleven still held sway in an extension of the Jewish program after the crucifixion and resurrection. They appealed to the nation of Israel to repent of the worst sin they had ever committed, killing their Messiah. Peter used the words, “You killed Him. You murdered Him.” God would yet pick up where He left off and send the king, and they could have the kingdom. Stephen also appealed to Israel to realize and believe that the one they had killed was indeed the Messiah, the Christ, the Son of the living God, but they stoned him.