This work of the young Joseph Ratzinger, now Benedict XVI, comprehensive treatise on ecclesiology, opens with a major study of its history, establishing the foundations of the church membership and outlines the doctrine of primacy. In the section devoted to studying the Church and its offices, you start seeing it in its origins, going back to it a divine institution and then examined in light of Pauline theology as a sign of faith and mystery. We study further the problem of belonging to the Church, based on the documents of the Magisterium, until the Second Vatican Council with its valuable contribution in this regard. New light, Ratzinger, delves into the concepts of primacy and episcopacy, and emphasizes the conciliar teaching on the collegiality of the bishops and implications of this doctrine. Noted theologian, then professor of dogmatic theology at the University of Regensburg, lays the groundwork for real reform in the Church, beginning with what is essential to any genuine reform: the internal renewal of the reformer, in this case of any Christian. In short, the book addresses, with full Christian responsibility, the doctrines that have caused more impact on the structure of the Church and her most urgent adaptations.