David Wells is a touch angry here, especially early on in the book. This one is the culmination of the series of books he's written over the years.
In short, he analyses prostestant Christianity as having split into three groups: the orthodox, those driven by marketing, and the emergents. The latter two - the dominant two - have given up the basics of Christianity and reintroduced a human-up spirituality, one in which we do not need the radical intervention of God.
Wells calls us back to basic biblical doctrines: the sovereignty of God in all things (including salvation), human inability to save, and confidence in the word of God.
This is not a book of methodology - and that's not meant as criticism. I guess Wells does not want us to fixate on the question 'What dod we do?', but return to the question, 'Why do we act?'