After he is miraculously released from prison, Peter goes to the home of Mary and her son John Mark. This seems to have been a larger home where people have gather to pray for him. While Peter had no problems getting out of the prison, he has some (humorous) trouble getting into the house where Christians are praying for him! (For this story as Greco-Roman Comedy, see J. Albert Harrill, “The Dramatic Function Of The Running Slave Rhoda (Acts 12.13-16) : A Piece Of Greco-Roman Comedy.” New Testament Studies 46.1 (2000): 150-157.)
Peter reports to this group what has happened (12:16-17). The scene inside the house is of chaos. Everyone is asking the same question: How did Peter get out of prison? Did he deny the Lord (again)? He explains to the group how the Lord rescued him. Peter tells the group to report to James what had happened. This request is unexpected at this point in Acts. The reader is not aware that James, the Lord’s brother is a believer. James will, however, become one of the major leaders of the Jerusalem church by Acts 15.
Jesus’ brothers did not believe he was the messiah during his ministry, but after the resurrection at least James and Jude come to understand what Jesus was. Paul reports a tradition 1 Cor 15:3-5 that Jesus appeared his brother James at some point. This may be a kind of commissioning to ministry since the other two named people on this list (Peter and Paul) are commissioned to a particular ministry. In church history, James has a reputation for being an extremely zealous Jewish believer and a leader among the Pharisees and priests who accepted Jesus (cf. Acts 21:18-25).
After asking for the group to inform James, Peter goes “to another place” (v. 17). This is rather non-specific way to conclude a series of stories about Peter, almost like “riding off into the sunset” at the end of an old movie. There are several possibilities for understanding the phase. First, it might mean Peter simply went to another location in Jerusalem. If he remained in Mary’s home, she could have been in danger for harboring a fugitive. Second, Peter may have left the region, out of Herod Agrippa’s jurisdiction, Keener suggests out of Palestine (2:1952). Third, a traditional view is Peter began travelling as a missionary like Paul will in the next chapter. This might take him as far as Corinth (1 Cor 9:5), Asia Minor (1 Peter 1:1) and possibly Rome. This tradition comes from Eusebius (H.E. 2.14.5). But since he is in Jerusalem in Acts 15, he does not seem to have gone far. Perhaps he only returned to the coastal plain and Caesarea, within easy travel of Jerusalem and later made Pauline-like missionary tours.
Fourth, some scholars see this as an indication of a shift in leadership in the Jerusalem community from Peter to James. Luke does have a tendency to briefly introduce characters who will be important later in the story, so there may be simply literary device like foreshadowing. It is fascinating to observe Peter’s absence from the book of Acts after this point, in contrast to James’ importance in chapters 15 and 21. James is not an apostle, but he does seem to be the leader of the Jerusalem community from this point forward.
It is also significant there is no effort to replace James the son of Zebedee after he is killed. On the one hand, it is at least 13 years after the resurrection, so the pool of individuals who could be witnesses from John the Baptist through the resurrection is diminishing. Even James the brother of Jesus does not qualify as a witness under those requirements!
All this seems to point toward a dramatic shift in the Luke’s story. He is concluding the first major movement of the book and preparing for Paul’s mission to the Gentiles in chapter 13.