Paul and Peter did not "preach" or "teach" to the same audiences. If you will examine WHO, WHAT, WHEN, WHERE and HOW (never WHY) for each of them, you will come to that understanding. Paul, after he "got his wings," taught that Jesus was the Son of God who sacrificed Himself for our original sin and our daily sins. His sacrifice was "willing," not because of murder. After being laid in the tomb He arose, and after 40 days, ascended to Heaven. We can receive Him if we will confess Him as Savior and Lord (John 3:3, Romans 10:8-13). That was the message for a Christian audience, not revealed to anyone but the Apostle Paul (Ephesians 3:9.) Peter, on the other hand, told the Jews (his audience) that they had murdered the Messiah (See Acts 2:22, and 29-38). Even though the 12, and most likely the 70, had been told in advance what was going to happen, they didn't accept it and rejected it (Peter is a good example, Matthew 16:21-23). They were not aware of the fact that Jesus was going to voluntarily go to the Cross! Take a look at Luke 18:33-34, and John 20:9, and the Acts references. Do that now, before you continue reading. Obviously, in the early chapters of Acts and in Matthew, Mark, and Luke, the 12+70 were unaware of Paul's gospel of salvation by grace through faith, the GIFT of God. They were still going about announcing the advent of the promised Jewish Messiah, having nothing to do with Gentiles and grace! After the ascension of Jesus Peter insisted that the Jewish people should repent (return to the Law and the oral traditions) and be ceremonially bathed, so that this same Jesus who had ascended would immediately return to establish the Kingdom of God, the 1,000 year Messianic Kingdom, with Jesus on the Throne (see Acts 3:19-21), a fulfillment of ancient prophecy. Paul was obviously the Apostle to the Gentiles (Acts 9:15, Romans 11:13). Peter was looking to the Law and to ritual, while Paul was saying to non-Jews that they were not under the Law and the traditions (Romans 6:14), and neither were the Jews, if they would accept Jesus Christ as Savior and Lord. Instead, the Jews rejected the Messiah and rejected Grace. If we Christians will get a grip on that, if we will "rightly divide" scripture, we won't have anything left to debate! We can then discuss, honor, and glorify our Savior!