Acts contains three stories woven into one:
When Jesus was crucified and rose from the dead, He had about 120 disciples (Acts 1:15). From that small beginning, Christianity soon grew to include thousands of people in cities scattered throughout the Roman Empire.
At first, all of Jesus' followers were Jews. Peter baptized the first Gentile Christian, Cornelius, but he continued to work mainly among the Jews. Many Jews did become believers, but most of the Jewish religious leaders rejected Jesus as the Messiah. The majority of the Jews followed their leaders and rejected Christianity.
A young man named Saul saw Christianity as a threat to his beloved Jewish religion and heritage, and he became a fierce persecutor of Christians. But Jesus appeared to Saul one day in a flash of bright light (Acts 9:1-6), and Saul was suddenly converted. Saul, later known as the apostle Paul, became the most energetic and successful Christian missionary of all! Although he was a Jew, Paul had his greatest missionary successes among the Gentiles. He traveled around the Mediterranean area preaching and establishing Christian communities wherever he went.
As great numbers of Gentiles became Christians, tensions developed between the Jewish and Gentile factions. Some Jews known as "Judaizers" insisted that the Gentile converts must observe all aspects of the Jewish Law, including dietary laws, Sabbath observance and circumcision. The dispute grew into a crisis that threatened to split the Church in two. Peter, Paul, Jesus' brother James, and other Christian leaders met at the "Council of Jerusalem" to resolve the issue. With the leadership of the Holy Spirit, the apostles formed a compromise solution which preserved the Church. They concluded that it was not necessary for the Gentiles to observe the Jewish Law in order to be saved. However, they did direct the Gentile Christians to avoid some actions which were particularly offensive to Jews (Acts 15:28-29).
As Christianity grew, tensions also developed between Christians and the dominant pagan culture. There were sporadic waves of persecution of Christians, particularly of the apostles and other leaders. Luke addressed both his gospel and Acts to a man named Theophilus, who may have been a Roman official. In both books, Luke tries to show that Christianity is not subversive and is not a threat to law and order in the Roman Empire (Acts 18:14-15, 19:35-41, 23:26-29).
The dominant theme of Acts is that Christianity is not just another religious sect. The growth and teachings of the Church were the work of God, acting primarily through the Holy Spirit. The Holy Spirit gave the timid and confused apostles wisdom, courage, power and words to speak (Acts 2:1-4). Divine intervention guided and protected the apostles at every critical junction in their ministry (Acts 4:8, 4:31, 9:10, 10:3, 10:9-15, 15:8, Acts 16:6, 16:9-10, 18:9, 20:23, 20:28, 21:11).
Most of our knowledge of the early decades of Christianity comes from Acts. Without that knowledge, we would have only a vague idea of how the tiny Jewish sect of Jesus' followers emerged into a major religion dominated by Gentiles. We are fortunate to have this book to help us understand the development of Christianity and to help us interpret the lives and teachings of the Apostles.