As the only record of the first thirty years of the early Church, the book known as The Acts of the Apostles, follows the ministry of the apostles, with a particular focus on St. Peter in the first half, and St. Paul in the second half. The author of the book is St. Luke the Evangelist, "the beloved physician" as St. Paul described him (Colossians 4:14), who was a companion of the apostles during several missionary trips; it was the second historical account written by St. Luke to a man named Theophilus (assumed to be a Roman officer), with the first account being the Gospel of St. Luke (after which Theophilus is presumed to have converted to Christianity).  This book, inspired by God, records for us the establishment and early growth of the Church, and relates several conversions (Ethiopian eunuch, St. Paul, and Cornelius). Without this work, we would be without an answer to "what happened next" after the gospel accounts, we would not have the context to help us understand many of the writings of St. Paul, and we would not have the benefit of seeing the Holy Spirit's work in the ministry of the apostles, as they fulfilled God's directive and theme of this book: "You shall be witnesses to Me" (Acts 1:8).