Why Acts? It follows perfectly from our extended study of Luke’s biography of Jesus, especially the transforming power of God’s Spirit in him, and what it means to be his disciples. Similarly, the snippet of Galatians, on the kinds of people we will find ourselves becoming, through that same indwelling Spirit.
It especially picks up from the Lord’s Prayer in Matthew 6: let it come, your kingdom; let the will of you come into being — as it already is in the heavens — also on earth. That’s the language of growth (just like Galatians’ fruit), and it's all about God’s action.
Acts, then, is exactly how this prayer gets answered — it’s all about God’s prior action in seeing his will being done among all people.