That said, Grabill's book can more than stand on its own. It is a work of true scholarship; its origin as a doctoral thesis means that it is not a breezy read. The scholarly apparatus is heavy, as it needs be, for Grabill is out to challenge the conventional wisdom.

The concept of “natural law” in Christian ethics is generally considered to be a Catholic way of thinking. The natural law does not refer to the law of the nature - where the strong lion eats the sick antelope - but to what reason alone, reflecting upon human nature, can conclude about how we should act. The argument is that it is possible to know that God should be worshipped or that stealing is wrong even without divine revelation - natural reason alone is sufficient to know such things. Such a law is “natural” as opposed to a manded law. The natural law tradition, which finds its biblical inspiration in Romans 2:15 - “the requirements of the law are written on their hearts” - was most carefully developed by Scholastic thinkers like St. Thomas Aquinas.

The usual telling of the tale is that the Protestant Reformers rejected the natural law tradition because it gave too much credence to the powers of fallen human reason, and not enough to the necessity of grace. While the Christian (Catholic) tradition never claimed natural law sufficient for salvation, the leading Reformation thinkers still thought that natural law thinking was not sufficiently Christian in the first place.

Except that they didn't. That's the argument Grabill is advancing, against several centuries of accepted thinking on that point, including the very negative assessment of natural law given by the Protestant theological giant Karl Barth in the middle of the last century. It is the bold doctoral student who decides to take on the heavyweights in his own tradition, and Grabill does so prudently. He does not argue so much that Barth and other contemporary Reformed thinkers are wrong as much he shows that it is they who have broken with their own Reformed traditions.

Does Grabill succeed? Ultimately, that will be a question resolved only if and when his work is accepted by contemporary Protestant moralists. But his detailed chapters on Reformation thinkers, beginning with John Calvin himself, are convincing enough on the major point: Calvin, Peter Martyr Vermigli, Johannes Althusius and others accepted and made positive use of the natural law tradition. It is hard to over-state the importance of Grabill's claim. If he is right - and this Catholic finds his documentation convincing - it opens the way to four potentially important initiatives.

First, it offers a prehensive moral theology to Protestants, precisely at a time when Protestants leaders are calling for a broader worldview, and a morality that is better grounded in metaphysics as well as Scripture (see the interview with Chuck Colson in this issue).

Second, it could be an exciting development in Catholic-Protestant theological dialogue. While recent years have borne witness to mon moral ground shared by orthodox Catholics and orthodox Protestants, the moral methodologies have remained quite different. Why we believe something is often as important as what we believe, and Grabill's re-interpretation of his own tradition will advance that conversation between Catholics and Protestants.

Third, natural law thinking, with its departure point of human reason and human nature, inoculates religious faith against fundamentalism, whether Catholic, Protestant or, for that matter, Islamic. Indeed, the possibility of reason as a ground of ethics opens the possibility of better cooperation between Christians and Muslims as a whole, leaving aside for the time being obvious disagreements on the content of divine revelation.

Fourth, natural law mitted Christians a vocabulary well-suited to exercising their vocation to contribute to mon good of society. Whether the issue is marriage or criminal justice or gambling, it is not persuasive to rely on biblical ethics alone in shaping public debate. Natural law provides an avenue for Christians to contribute to public debates precisely as citizens, without asking for any special privileges for Christian revelation.

All of that is too much to ask from one book. But from time to time a book can advance significantly a promising argument, and Grabill's book is just that, in arguing that the arguments of the Reformation may not have been as divisive as has been long thought.