I read this as part of the theological mentoring program I'm participating in over the last couple of years. This is one of the books we're reading about the nature of the Church, and in particular Twelftree explores the what Luke articulates in his Luke-Acts writings.
In this book, Twelftree wrestles with a number of the classic church questions: what is the nature of the church? What is the nature of the relationship between the church and salvation? How does the Spirit and things like the gift of tongues fit in? What did worship look like? How did the early church understand Scripture? What was their mission as they understood it? Throughout, Twelftree carefully and methodically examines what Luke was trying to say and how it lines up with what the church presently believes.
On the whole I found the tone of the book just a bit dry for me (reads like a scholastic book even a bit more than I'm used to), but I did find some of his conclusions quite interesting. The way he articulated the early church's understanding of Scripture (less prescriptive and more used in making sense of their ongoing experience of Jesus in their midst and the leading of the Spirit) was rather daring conclusion, as was his conclusion on mission (that the church needs to stop preaching the gospel to itself and bringing social action to the world and work to preach the gospel to the world and bring social action to the church). I'm glad for his summary chapter at the end which I suspect I'll continue to chew on for a while.
People wanting to give a serious scholastic-level examination of the nature and functions of the church according to the New Testament. You need to be able to wade through it, but there is good content here.