The purpose of this book is to shed light on the thought of Dirk Philips, who was a Mennonite leader in the sixteenth century, and to argue that his various doctrines, including his Christology, ecclesiology, soteriology, and anthropology, are interrelated with his view of the visible church. This book explains that Dirk Philips’ view of the visible church is much closer to the ecclesiology of Augustine’s tradition rather than to the ecclesiology of the Donatists’ tradition. Although Dirk Philips had excellent theological abilities and he was a leader who made a significant contribution to the development of the Mennonites camp, he did not receive much attention in the study of Anabaptists, and there has not been much research on this sixteenth-century Mennonite leader. Thus, this book will help you discover a great sixteenth-century leader who has been forgotten in church history. Is it true that the Radical Reformers are disciples of Donatus, that the Anabaptists thought that the failed believers cannot be forgiven because the church is a gathering of pure souls? This book will probe the idea that the Radical Reformation is closer to the ecclesiology of Augustine’s tradition than to the ecclesiology of the Donatists’ tradition.