Book excerpt: One of today's leading theologians tackles some of the most significant themes in contemporary theology. Douglas Farrow explores key theological loci such as nature and grace and justification and sanctification; introduces theological giants such as Anselm, Aquinas, Luther, and Barth; and examines contemporary questions about sacraments and unity. Throughout his explorations, Farrow invites readers to consider how to negotiate controversy in Christian theology, especially between Catholics and Protestants, arguing that theology does its best work at the intersection of topics in dispute.