In this remarkable work Michael O'Neil investigates Karl Barth's theology in the turbulent and dynamic years of his nascent career, between 1915 and 1922. It focuses on the manner in which this great theologian construed Christian and ecclesial existence. The author argues that Karl Barth developed his theology with an explicit ecclesial and ethical motive in a deliberate attempt to shape the ethical life of the church in the troublesome context within which he lived and worked. O'Neil adopts a chronological and exegetical reading of Barth's work from the initial dispute with his liberal heritage (c.1915) until the publication of the second edition of his commentary on Romans. Not only does this work contribute to a broader understanding of Barth's theology both in its early development, and with regard to his ecclesiology and ethics, it also provides a significant framework and material for contemporary ecclesial reflection on Christian identity and mission.