Paul for a time tolerates the witness to the gospel exclaimed by a slave girl. However, he is well aware that she is inhabited by a demonic spirit. He presumably decided that it would harm the mission if the gospel was being spread by such a person as this diviner, especially as God had clearly shown his hatred of the whole business of using mediums to see the future. Getting back to the task in hand, Paul and Silas have false charges laid against them and are detained in prison. They will, though, get out of that place and preach the gospel which gives repentant men and women not a familiar spirit but the Holy Spirit.