What does Acts 12:18 mean?

Until the evening before, Peter had been a prisoner of Herod Agrippa I in Jerusalem. Agrippa had arrested and beheaded James, the brother of the apostle John—an act which earned the Sanhedrin's approval. Ever looking to ingratiate himself with the local leaders, Agrippa arrested Peter, as well, and had intended to execute him the day after the weeklong Feast of Unleavened Bread. Before the soldiers could bring Peter from his jail cell, however, an angel rescued him (Acts 12:1–11). Peter stopped by the home of Mary, whose son is John Mark, before going into hiding (Acts 12:12–17). We will hear of Peter only once more in the book of Acts—in the Acts 15 meeting regarding how much Gentile Jesus-followers should accommodate the practices of their Jewish fellow believers.

The guards, understandably, are confused and not a little frightened. When the angel came, Peter was asleep, chained up between two soldiers, with at least two others standing between him and the gate (Acts 12:6). This is eight to fourteen years after soldiers were involved in guarding Jesus' tomb. We don't know the specifics of the events, but we know the Sanhedrin sealed the stone blocking the doorway of Jesus' tomb and set up a guard of soldiers to keep the disciples from stealing His body (Matthew 27:62–66). The next morning at least one angel appeared, rolled back the stone, and took a seat. The soldiers "trembled and became like dead men" (Matthew 28:2–4). We don't know if that means they became insensate or if they were just paralyzed yet completely aware of their surroundings. When they reported what had happened to the priests the Sanhedrin bribed them to say they had fallen asleep (Matthew 28:11–15).

To fall asleep during guard duty was punishable by death, but their assignment was for the chief priests of the Jews, not Pilate or any other Roman official. The chief priests at the time of Jesus' resurrection told the solders they would take care of any difficulties they might have with the governor and keep them out of trouble. This time, the soldiers' supervising authority is no less than the king. Unlike Peter, they will not escape unscathed (Acts 12:19).

Years later, Paul will experience something similar with a very different reaction. He and Silas will be beaten and jailed in Philippi when an earthquake will open the doors and break the shackles of all the prisoners. But when the jailor arrives, fearing for his life if the prisoners are gone, he will find them sitting patiently. He will see to Paul and Silas' wounds and hear the story about Jesus. Peter serves God's kingdom and purposes by escaping. Paul and Silas do so by staying and introducing the jailor and his household to Jesus' saving grace (Acts 16:25–34).