How can the church start at Pentecost? If it was something new, why were three thousand ADDED to the church? Peter at Pentecost is not telling Israel that Jesus died for their sins. He’s telling them they killed their Messiah. He’s not preaching the cross as good news. He’s preaching a murder indictment against Israel.
1 And when the days of the Pentecost were accomplished, they were all together in one place: 2 And suddenly there came a sound from heaven, as of a mighty wind coming, and it filled the whole house where they were sitting. 3 And there appeared to them parted tongues as it were of fire, and it sat upon every one of them: 4 And they were all filled with the Holy Ghost, and they began to speak with divers tongues, according as the Holy Ghost gave them to speak. (Acts 2)
The sermon of Peter, one of many, follows. But it is not true that it is only an indictment of the Jews, it also proclaims the gospel forcefully:
21 And it shall come to pass, that whosoever shall call upon the name of the Lord, shall be saved. 22 Ye men of Israel, hear these words: Jesus of Nazareth, a man approved of God among you, by miracles, and wonders, and signs, which God did by him, in the midst of you, as you also know: 23 This same being delivered up, by the determinate counsel and foreknowledge of God, you by the hands of wicked men have crucified and slain. 24 Whom God hath raised up, having loosed the sorrows of hell, as it was impossible that he should be holden by it. 25 For David saith concerning him: I foresaw the Lord before my face: because he is at my right hand, that I may not be moved. 26 For this my heart hath been glad, and any tongue hath rejoiced: moreover my flesh also shall rest in hope. (Acts 2)
Here it is, the entire gospel of salvation.