Paul moves from preaching in Asia to now preaching in Europe. He is put in prison for his faith. So the one who had put Christians in prison is now the one in prison. Even when in prison, Paul looks for ways to bring people to Jesus.
Paul’s message to the jailer in verse 31 is a simple one. The message of Jesus isn’t complicated, but still people struggle to understand it. How can something as valuable as forgiveness be available to anyone simply by believing?