There are several reasons why Luke wrote the Book of Acts. There were many false stories about the Christians. The people that were telling these stories were afraid that the Christians wanted to cause trouble. Luke wanted the Roman authorities to know that this was not true. Christians helped people to behave well. Luke wanted to show the authorities that their practice was good for the Roman government.
Every paragraph in this book is related to the church witnessing for Christ. The author is continually concerned with the history of the early church. The description is not on local church organizations but a view of the unique body in which Jews and Gentiles were united on a perfect equality. The union of such had been intimated by Christ, (John 10:16) but the mystery of this body was not revealed until after His resurrection. (Ephesians 3:6) The book of Acts shows how this body came into being. Acts describes how the church gradually came from a local sect into a universal brotherhood. Christianity was emancipated from Judaism and became a worldwide religion. The author follows the church’s growth throughout the empire from Jerusalem to Rome. He shows how the Christian faith embraced representatives of many nationalities and always remained as a united body.