O'Donovan argues that "evangelical" ethics is ethical living in light of the renewed and renewing creation. The created order--the order of creation, the purpose for which it was established--is vindicated in the cross/resurrection of Christ and is given back to God's people. Although the point is not specifically made, it seems O'Donovan is stressing a teleological ethic (although I wouldn't pin him down on such).
He then proceeds to critique historicist ethics, particularly the Marxist form. Following, he argues that a corollary of ethics is epistemology: the Christian's knowledge is in key and in part a *knowledge in Christ.* While not a primary or exhaustive part of knowledge, *experience* is a factor in knowing. For the Christian knowledge often comes in light of suffering and the way of the Cross (my favorite part of the book).
I found his section on "eschatology" most compelling and most underdeveloped. He seems to posit a realized eschatology. This is good. He anticipates on one hand the coming resurrection but also the the powerful in-breaking of the eschaton into the present order (see thesis of book). Some excerpts:
The resurrection of Christ redeems and transforms the created order (56).
The work of the Holy Spirit defines an age--the age in which all times are immediately present to that time, the time of Christ (103)
The book left me with questions concerning "what to do?" Having read it, what should be my response? This is probably the fault of the reader, and thus I need to reread it.
I wasn't quite clear of his criitques of natural law. I was interested in a critique of natural law theories, and he gave some, but I couldn't make sense of them (again, my fault and not OO). On the other hand, however, his critique of the Roman Catholic sexual ethic, based on natural law, was quite good.