The second half of the book of Acts is dominated by the scene of the council in Jerusalem in chapter 15. The dispute over circumcision is a dispute over whether faith in Jesus as the Messiah is a new version of Judaism or something else entirely. If Gentiles, non-Jews, who are brought to Christ through the preaching and miracles of the apostles must be circumcised before being baptized, then the followers of Christ are saying that they are still Jews. Paul and Barnabas have been arguing against this practice, and in Luke's telling here Peter positions himself as the one initiating the mission to the Gentiles and as standing against circumcision. Paul's view of this dispute, which we will encounter when we read his Letter to the Galatians in a few weeks, is rather less generous to Peter. Whatever the historical truth, the important point is that the decision by the leaders depicted here – first Peter, and then James (known as James of Jerusalem, the brother of Jesus) – marks an assertion that Christianity, not yet really so named, is a new movement, a new faith, and something separate from its Jewish heritage. While the Pentecost event narrated in the second chapter of Acts is celebrated as the birth of the Church because of the gift of the Holy Spirit, this council's decision is perhaps the more definitive birth of the Church as a distinct new faith and a separate institution.
The rest of Acts builds on this decision, as it follows Paul on his many trips to found churches or to visit again those already founded. An intriguing aspect of his many speeches in these latter chapters is his willingness to adapt his message to his audience: the sermon on "the unknown God" he delivers in Athens (17:22-31) is radically different from his exhortation to the church in Ephesus (20:17-35) or again from his personal faith story as delivered to Festus and Agrippa (26:1-23). We will see this ability as we read his letters to various churches – Paul's great gift of seeing what aspects of the faith are most useful or applicable in specific life situations is on full display in these chapters and gives us a great view of the rapid growth of this strange new faith.