For many years scholarly interest in Martin Bucer was limited, for the most part, to his political role during the early decades of the Reformation, as a mediator between the rival Protestant centres of Wittenberg and Zurich. Recently, however, there has been growing appreciation of Bucer's achievement as a theologian in his own right, with a lasting impact on the Reformed tradition, in particular. An important milestone in modern Bucer research was Martin Greschat's biography of the reformer, which first appeared two decades ago. Now Greschat, one of Germany's leading church historians, has published a second, fully revised edition of the work drawing on more recent scholarship, especially the on-going editions of Bucer's German and Latin works and correspondence.

In his account of Bucer's intellectual formation, Greschat highlights two key influences: the Thomism of the Dominican order, into which Bucer was received in 1508, and the writings of Erasmus. Although the catalyst for Bucer's break with Rome was an encounter with Luther, at the Heidelberg disputation in 1518, his mature theology remained indebted in many respects to both Aquinas and Erasmus. Thus while Bucer embraced the doctrine of justification ex sola fide, the sense of opposition between Law and Gospel that so dominates Luther's thought is largely absent from his theology; instead, he saw the justified believer as internalising the Law, through the power of the Holy Spirit, and thereby becoming a new creature. In his emphasis on the ethical dimension of soteriology, Bucer harks back to Erasmus and anticipates Calvin. As Greschat points out, Erasmus also helped to shape Bucer's understanding of marriage as companionship, leading him – uniquely among sixteenth-century reformers – to propose that the breakdown of a relationship be accepted as grounds for divorce.

The impact of Erasmus' thought on Bucer is perhaps most evident in the latter's commitment to Christian unity. Initially, Bucer's efforts in this direction were confined to his fellow Protestants, but from the end of the 1530s he turned his attention to the still more daunting task of dialogue with Rome. Greschat provides an excellent account of Bucer's collaboration with reform-minded Catholics such as Georg Witzel, Johannes Gropper and, most famously, Gasparo Contarini, at the colloquy of Regensburg. This approach came closest to bearing fruit in the archdiocese of Cologne, where Hermann von Wied sought to implement a Bucerian-inspired programme of religious reform. As Greschat makes clear, it would be wrong to attribute Bucer's irenicism to a lack of theological seriousness or solidity; even at Marburg he did not disguise his preference for Zwingli's understanding of the eucharist over that of Luther. Unlike most of his contemporaries, however, Bucer held that even quite significant theological differences could be accommodated within the same ecclesial community, in line with the fundamental emphasis in his theology on the primacy of the spirit over the letter.

Another area to which Greschat devotes considerable attention is Bucer's ecclesiology. Bucer conceived of the Reformation as a project for the transformation not just of individuals, but of society as a whole, which he aspired to bring under the ‘rule of Christ’ (significantly, the title of his last major work). Like other mainstream reformers, he was hostile to Anabaptist calls for withdrawal from the world, believing instead that a new social and moral order could be brought into being with the support of the secular authorities. In Strasbourg, however, this vision of a more godly society was never shared by the city council, which resisted the demands of Bucer and his fellow pastors for the implementation of biblical law and Christian discipline. Eventually, out of frustration, Bucer resorted to setting up a parallel ecclesiastical jurisdiction in the city, made up of so-called ‘christliche Gemeinschaften’ that operated within existing parish structures. Bucer never abandoned his commitment to magisterially-led reform – he understood the ‘christliche Gemeinschaften’ not as stand-alone bodies but as precursors to a more thoroughgoing transformation of the Strasbourg Church – but his experience exposed a fundamental and recurrent tension within mainstream Reformation thought. Ultimately, the ‘christliche Gemeinschaften’ served as a model for the sort of semi-autonomous church governance that, as further developed by Calvin, was to have a long history in Reformed Protestantism.

Greschat provides a wide-ranging and comprehensive survey of Bucer's career, accessible to the general reader as well as to specialists. Despite failing to leave behind a distinct theological ‘school’ associated with his name, Bucer is shown to have influenced key aspects of Reformed teaching, especially in relation to the eucharist and church discipline. Greschat also highlights the international reach of Bucer's activity, which extended beyond Germany to the emerging evangelical communities of France and Italy and, in the final months of his life, the England of Edward vi. Without seeking to gloss over Bucer's weaknesses – his notorious verbosity, his hostility towards the Jews and his Puritanism, which so antagonised the Strasbourg authorities – Greschat overturns the traditional view of Bucer as ‘einem glatten Taktierer und wortreichen Opportunisten’ (p. 119), characterising him instead as a ‘Theologe des Dialogs’ (p. 284). As Greschat demonstrates, the very features of Bucer's personality that made him controversial in his own time – his recognition of difference and willingness to go the extra mile for the sake of religious unity – are those that make him appear so ‘modern’ and sympathetic today.