The book presents the transition from traditionalism to modernism in connection to two of Küng's most important books on ecclesiology: Structures of the Church (1962) as representing Küng's traditional theology, and On Being a Christian (1974) as a reflection of his modern approach to Christianity.

This Reader presents a cross-section of ecclesiological statements from across the centuries of the church's existence. It builds on the foundations of early Christian writings, illustrates significant medieval, reformation and modern developments, providing a representative look at the robust attention to ecclesiology that characterizes the contemporary period. This collection of readings offers an impressive overview of the multiple ways Christians have understood the church to be both the 'body of Christ' and at the same time, an imperfect, social and historical institution constantly subject to change.