What does Acts 13:15 mean?

Paul and Barnabas are in Pisidian Antioch, slightly southwest of the center of modern-day Asia Minor. The Holy Spirit chose them to spread the news about Jesus specifically to the Gentiles. However, in keeping with Jesus' commission (Acts 1:8), whenever he and Barnabas reach a new town they always start in the Jewish synagogue.

The Israelites spent much of the Old Testament confused as to where to worship God. Until Solomon built the temple, many people sincerely sought God's guidance in one of the many "high places." Upon Solomon's death and the split of the nation, Jeroboam, king of the northern kingdom, set up two golden calves for the expressed purpose of preventing his people from traveling to Jerusalem to sacrifice to God (1 Kings 12). In the ensuing centuries, the southern kingdom of Judah periodically lost their copies of the Mosaic law. Neither kingdom emphasized the proper worship of God.

It wasn't until their exile in Babylon that the southern kingdom of Judah grew to seriously value the Law and how the Law identified them as a people. The exiles started meeting in assemblies or "synagogues" to read from the Scriptures and discuss the text. Often, the synagogue leader would ask a well-educated visitor to speak and provide a different point of view. Paul, who had been trained by the famous Pharisee Gamaliel (Acts 22:3), took advantage of this custom by showing how Jesus of Nazareth fulfilled the prophecies given in the Prophets. Despite Paul's many visits to different synagogues, the message he gives in Pisidian Antioch is the only one Luke records.