Acts 19-28: Moving from Proclamation to Defence of the Gospel
I have long found David Gooding's book, True to the Faith, a really helpful look at the book of Acts, mapping out how Luke's story unfolds and how it teaches us in the process.
As I look at chapters 19-28, he introduces his section on this with the following really helpful paragraph (page 338 in my 1990 edition; I'm not sure how much material has been added by the currently in-print 2013 edition to move the page numbers on):