Written over three decades ago, Cardinal Ratzinger’s profound treatise on the true meaning of Christian brotherhood is perhaps even more timely and important now as a clear statement on the biblical grounds for cooperation among believing Christians. In treating Christian brotherhood from the perspective of salvation history, Ratzinger opens up the meaning of both the Old and New Testament in this most essential area. After establishing the distinctively Christian sense of brotherhood (vis-a-vis Judaism, Hellenism, Stoicism, the Enlightenment, and Marxism), he shows how fraternal charity can only be perfected through God’s fatherhood, Christ’s divine sonship, and our brotherhood in Christ.