The document discusses the events surrounding Pentecost, a Jewish feast celebrated fifty days after Passover, during which the Holy Spirit descended upon the apostles and other followers of Jesus who were united in prayer. This event marked the beginning of the Christian mission as the apostles received the ability to speak in various tongues, enabling them to spread the gospel to a large number of Jews present in Jerusalem. The narrative emphasizes the connection between the giving of the law at Sinai and the outpouring of the Holy Spirit, illustrating a transition from the Old Covenant to the New Covenant in Christianity.