This book, which Hans Küng has dedicated to Dr Michael Ramsey, is his major work on the nature of the Church, and provides a comprehensive picture of its theological image as expressed in the historical forms it has taken through the centuries from the present day back to its origins.
As Hans Küng notes in his Preface, there is much talk nowadays about the Church in the secular-world but not a corresponding awareness of what the Church is. To know this we have to know what the Church was originally, and on investigating this we find that the New Testament provides no doctrine of the Church's essence that preceded her initial form. From this it is concluded that essence and form cannot be separated, that the real essence of the real Church is expressed in historical form. But essence and form are not identical so impatience with the theological image of the Church – as we find it expressed today, for instance – need not necessarily lead to departure from the institution. Hans Küng's systematic approach through history to the Church's origins, in which he notes the various forms that it has taken since, uncovers for both Protestant and Roman Catholic some vital lessons about the community to which he belongs and about how Christian theologies might view and approach its future as a visible institution. Jesus said he would be with mankind always. Instead of fearing that radical reform will obscure his presence, we should pursue it in the interests of his promise, knowing that this promise is the guarantee of ultimate validity.
In this spirit, and with his customary thoroughness, clarity and objectivity, Hans Kiing reveals the essential ecclesiological threads that if grasped and understood will enable the Christian Churches to approach the future more confidently, and in doing this he takes a most important step towards the clarification of the many issues that at present complicate the ecumenical encounter. Fundamentally he is concerned with the credibility of the Church in the modern world and to this end shows what is permanent and essential in it and what historically conditioned. The four signs of the Church, unity, catholicity, sanctity and apostolicity, and its significance and structure, especially with regard to ecclesiastical office, are examined in relation to the present, and in relation to the need for the reconciliation of the Christian Churches. As such it is an important contribution to the encounter between Christian theologies. He concludes his Preface by expressing the hope that "there lies within the pages of this book a theological basis for a rapprochement between the Church of Rome and Canterbury."