The Monothelete controversy has until recently been one of the least studied episodes in the development of Christian dogma. The debate on the number of activities and wills in Christ provoked a schism in the imperial Church in the seventh century, with the doctrine of two activities and two wills eventually endorsed as orthodoxy at the sixth ecumenical council (680–1). Only recently have historians and theologians come to realise that the view attributing to Christ one activity and one will also belonged to the mainstream of Chalcedonian theology. Christian Lange's monograph is an important step in this reappraisal of the Monothelete controversy. He draws a sharp distinction between the earlier stage of the controversy, when the doctrine of the single activity of Christ served as a theological basis for the emperor Heraclius (610–41) and the patriarch of Constantinople Sergius (610–38) in their efforts to restore the unity of the Church, and the later controversy on the number of wills, which was an internal Chalcedonian discussion. Lange's interests lie in the first, Monoenergetic – he prefers the word ‘Miaenergetic’ – stage of the controversy.

This remarkably well researched book is structured in five chapters. Over two-thirds of the book are occupied by the first chapter, retracing the Christological controversies in the Roman Empire from the Council of Chalcedon and the efforts to heal the growing rift within the Church (pp. 21–470). The two following chapters offer historical and theological overviews of the Churches of Persia (pp. 471–516) and Armenia (pp. 517–30). The book culminates in the fourth chapter, dedicated to the ‘Miaenergetic union policy of the emperor Heraclius’ (pp. 531–622), and ends with a brief summary (pp. 623–30). Despite the subtitle (‘Studies on the union policy of the emperor Heraclius and of the patriarch Sergius of Constantinople’) and the declared subject of the book, the analysis of the ecclesiastical policy of Heraclius thus occupies a mere hundred pages, with the bulk of the book dedicated to a survey of Christological positions of the fifth and sixth centuries. This long introduction serves to present the doctrine of one activity as the logical outgrowth of the Neo-Chalcedonian emphasis on the hypostasis as the acting subject of the Son of God. The perhaps more demanding task of identifying the antecedents of the doctrine of two activities is, on the other hand, left unaddressed. The reader is also surprised by the decreasing detail of coverage as the narrative approaches the times of Heraclius: while Lange dedicates a significant place to the reign of Justinian, he deals with Heraclius’ predecessors – Justin ii, Tiberius, Maurice and Phocas – in six pages. An evaluation of the hands-off ecclesiastical policy adopted by Maurice, for instance, would enable a better understanding, by contrast, of the activism of Heraclius.

The analysis of the union policy of Heraclius and Sergius is the most interesting and the most rewarding part of the book. Lange strongly emphasises the ‘erstaunliche Erfolg’ of Heraclius’ ecclesiastical policy that led between 629 and 633 to the restoration of ecclesiastical communion with the ‘Severian’ Churches of Syria and Egypt, as well as the Church of Armenia and the Persian ‘Church of the East’. This is an important argument, seldom voiced in such a consistent and forceful way. Lange is also one of the first theologians to give attention to the Synod of Cyprus known from the Syriac Life of Maximus the Confessor. He dates it to 634 and proposes to identify the imperial edict issued in its wake with the Psephos. This is an intriguing possibility, but it would benefit from a deeper discussion of the chronology, as the sequence of events presented by Lange is not intuitive: it can be objected that Sophronius' letter to Arcadius of Cyprus seems to have been penned after, and not before, his election as patriarch of Jerusalem. It is also unclear why Lange assumes Sophronius' synodical letter to have been composed after the Synod of Cyprus.

The chapter on Heraclius' union policy, and indeed the entire book, rests upon the assumption that the ecumenical efforts of the emperor were based on the concept of one activity of Christ, developed in order to bridge the Christological gap between the imperial and the non-Chalcedonian Churches. It is difficult to disagree with Lange that, from the Chalcedonian perspective, the formula of one activity was well suited as a starting point for the ecclesiastical unions. But Lange constantly runs into trouble when he tries to see this formula in operation: the two earliest Chalcedonian sources on the union with the Jacobites, Antiochus Monachus and Euboulus of Lystra, do not make any reference to the activity; the statement of faith of the Persian catholicos quoted in connection with the union with the imperial Church does not mention activities; the activities played no role in the union with the Armenians; and they are at best secondary in the document of union with the Egyptian Theodosians. Even if the concept of mia energeia is not altogether absent from the unions, it does not appear to be central to them. Should we conclude that Heraclius' union policy was based on a mixture of personal prestige, the carrot-and-stick approach, and willingness to make non-vital theological concessions, rather than on a dogmatic innovation? This possibility should be given serious consideration now that we realise the extent to which the narrative of a theological innovation aimed to entice the dissidents into union with the imperial Church was the creation of Sophronius, Maximus the Confessor and their circle.

This book, in conclusion, usefully combines a historical and a theological approach in the study of the Monothelete controversy. It is to be hoped that it will stimulate more debate from both historians and theologians.