Rowan Williams, the archbishop of Canterbury, is caught in the crossfire between warring parties in the Anglican Communion. They are fighting over how the church relates to sexuality, to Scripture, and to the church's member bodies.

In his new book, Why Study the Past?, Williams does not address the dispute head on. Instead, he says that Christians should be "looking and listening" in their "study of Christian history for what feeds and nourishes belief now."

This study should unsettle both traditionalists and progressives, he says. Progressives, Williams chides, don't expect to be interested in or questioned by history. But Williams admonishes traditionalists as well: We "don't expect to be surprised by the past."

Williams examines how the early church handled the fact that, in Jesus, everything had changed, while at the same time, it did not discard everything that came before Jesus. The earliest Christian disputes were over the degree of continuity between Judaism and the Jesus movement, and the degree of discontinuity brought by the final revelation and full atonement experienced in Jesus. Read Christian writers of the first few centuries with that in mind, and you'll see a community lurching from one end of the spectrum to another before finding an appropriate middle ground.

The Reformation comes in for similar analysis. The weakened political state of the late medieval church allowed critical thinkers to question its relationship to civil power. Luther's theology is not, Williams says, "a bid for individual freedom of conscience." Instead, it is "a protest against the belief that conscientious scruple can be solved by immediate human authority. … What it places at the center of everything is the gratuity … of ...