What does Acts 13:40 mean?

"Beware," or "take care," starts the last of the five sections of Paul's sermon. It is the only synagogue message whose words Luke recorded. Paul and Barnabas are in Pisidian Antioch, speaking to a group of Jews and God-serving Gentiles. The group knows of John the Baptist, how he exhorted people to repent of their sins. They either do not know of Jesus, or they do not know who He really is and what He came to do.

Revealing this is the purpose of Paul's message. He started with an overview of how God saved the Jews in the past and His promise of a Savior to come (Acts 13:16–25). Then he told Jesus' story (Acts 13:26–31) and explained how the Scriptures validate that story (Acts 13:32–37). The fourth, and most difficult, section dealt with a redefinition of God's "salvation"; in the Old Testament, God saved His people from slavery, enemies, and hardships—now He will save them from their sins (Acts 13:38–39). Finally, Paul warns them to accept what the prophets had said.

The message of the prophets has always been that obedience to God brings blessing, disobedience brings curses, and repentance brings restoration. This verse introduces verse 41: "Look, you scoffers, be astounded and perish; for I am doing a work in your days, a work that you will not believe, even if one tells it to you." It is a quote of Habakkuk 1:5, but from the Septuagint which has slightly different wording.

Although the context of Habakkuk doesn't exactly match that of Paul's audience, the meaning stands. God is doing astounding work by sending Jesus to save the people from their sins. It will be very difficult for the Jews to accept this, but those who scoff at His offer will perish. This group of Jews and Gentiles who read from the prophets every week should be able to see how Jesus of Nazareth fulfills the prophecies they are reading. Some will, but some will succumb to jealousy and reject their intended Savior.