Luke picks up where he left off from his gospel  with what happened after Jesus ascended. The book is written as a narrative so the many of the same principles would apply as the ones we looked at for Old Testament narratives. 
Luke records how the gospel went out, empowered by the Holy Spirit and results in changed lives and changed communities. This is God’s purpose for the  church today - the forward moving growth of the gospel empowered by the Holy Spirit.