He traveled around the Roman Empire, teaching others about Christianity, and wrote letters back and forth with the churches he helped to begin. The letters contain many important parts of Christian teaching and have since been part of the New Testament of the Bible, coming between the Acts of the Apostles and the General Epistles. It is not known whether Paul actually wrote all of these letters, or whether other people could have written the letters for him. Part of these letters are read at Mass as the second of two readings that come before the Gospel.