Zurich’s role in the early development of Reformed theology is frequently underestimated, especially (but not exclusively) due to the prioritization that scholars have sometimes given to other Reformed hubs like Geneva or Heidelberg. Pierrick Hildebrand’s (University of Zurich) recently published doctoral thesis, The Zurich Origins of Reformed Covenant Theology, is a full-throated corrective that argues for the centrality of Zurich (i.e., Zwingli and Bullinger’s roles) in the development of Reformed Covenant Theology.

The monograph is broken into three distinct sections, with the first two sections occupying the central core of his argument. Part 1 (chs. 1–2) investigates the distinctly Zwinglian origins of Reformed covenantal theology. Part 2 (chs. 3–5) explores Bullinger’s development of Zwingli’s inchoate doctrine into a central theological theme, while arguing that it was these very developments that allowed Bullinger to be a major player in the consolidation of the Reformed tradition. The final section, part 3 (chs. 6–7), explores the reception of Bullinger’s covenantal theology in both Geneva and Heidelberg.

The first central argument of this book, explored in part 1, argues for a Zwinglian priority for the beginnings of Reformed Covenant Theology by examining Zwingli’s works from 1519 to 1525, which showcased a theme of discontinuity between the Old and New Testaments and the early elements of Zwingli’s break with the Roman Catholic Church (ch. 1). Hildebrand describes the year 1525 as the “Covenantal Turn” of Zwingli’s theological career, pointing not to the Anabaptist controversy as the emerging context for this development (i.e., Gottlob Schrenk’s traditional thesis that rests on works developed from 1526 and onward), but rather within the context of his polemic against the Roman Catholic view of the Lord’s Supper. He bases this on what he sees to be “a hermeneutical move from an analogical to a univocal view of the relation between the Abrahamic covenant and Christ’s new testament” (p. 59) in Zwingli’s relatively unstudied work on the Eucharist, the Subsidium (August 1525). Zwingli, Hildebrand argues, continued to sustain this idea of covenantal continuity throughout the course of his career, and in turn, he granted Bullinger vital resources for the development of his own covenantal thinking.

From here, Hildebrand dedicates three chapters to a comprehensive treatment of Bullinger’s works and his development of Zwingli’s ideas, describing these central chapters as “the heart of [his] study” (p. 111). Bullinger did not simply repristinate Zwingli’s ideas; rather he cultivated and continued Zwingli’s Covenant Theology by imbuing it with two intimate and indissociable elements: the “historical-legal” aspect and the “organic-mystical” aspect. The former matter is one shared between Zwingli and Bullinger; it represents the “redemptive-historical unfolding of the one covenant of grace, which culminates in Christ’s vicarious atonement and implementation of his testament through his death” (p. 111). The latter aspect is much more unique to Bullinger in that it is described as the communal and spiritual life of God’s covenant people made manifest through union with Christ. In other words, within Bullinger’s developing theology, “the covenant is ultimately identified with union with Christ” (p. 202), which “enlarged” (p. 238) the legal aspect of Zwingli’s Covenant Theology. This twofold understanding of Bullinger’s Covenant Theology, according to Hildebrand, poses a challenge to the idea that Bullinger held to either a unilateral or bilateral covenant, as contemporary scholarly debates continue to insist. As such, Hildebrand suggests that there is far more continuity not simply between Zwingli and Bullinger, but also between Bullinger and Calvin.

The final section moves beyond Zurich as Hildebrand argues that both leading theologians in Geneva (i.e., Calvin) and Heidelberg (i.e., Ursinus and Olevianus) openly adopted insights from Bullinger’s covenantal theology. In the case of John Calvin, Hildebrand emphasizes that Calvin integrated the twofold dimensions of Bullinger’s covenantal theology directly into his own. Geneva and Zurich, then, should not be viewed as rivaling traditions but as a shared partnership in the development of Reformed Covenant Theology. Finally, he argues that Bullinger’s theology was also adapted by Zacharias Ursinus and Caspar Olevianus, making it plausible that both Calvin and Bullinger provided a “common body of thought” for these Heidelberg theologians (p. 291).

It is no surprise that Hildebrand’s monograph was awarded the REFORC Book Award of 2025. His central theses are thoroughly convincing and present a helpful corrective to certain narratives of the early Reformed tradition. There is simply one qualification I would make to a subsidiary argument in Part 1. In the attempt to dispel the idea that Zwingli’s covenantal theology emerged as a reactive solution to the Anabaptism controversy, Hildebrand downplays that controversy as the contextual origin for Zwingli’s “covenantal turn.” While this is partly true, Zwingli had written his Von der Taufe (May 1525) just three months prior to the Subsidium (August 1525), and Balthasar Hubmaier had just published his On the Christian Baptism of Believers, criticizing Zwingli, on 11 June 1525. In my view, it is better understood as having emerged in a shared context of sacramental polemics emanating from Zwingli’s distinctive hermeneutic.

That minor point aside, his section on Bullinger is a masterclass in primary source engagement. Among these sources are an assortment of archival materials, understudied exegetical materials, and sermons. His careful, close readings of primary sources are a reminder of the fruitfulness of returning to the sources themselves. This book is essential reading for any theologically trained person who wants to understand the roots, the reception, and, I would argue, the very heart of Reformed Covenant Theology.