Nestor Kavvadas, a scholar of Syriac Christianity and currently a research assistant at the Faculty of Catholic Theology at Tübingen University, proposes in the monograph under review a historical and theological contextualisation of the cardinal aspects of the doctrine of Isaac of Nineveh (seventh century). Isaac was the most influential of Syriac Christian authors, managing to transgress the ecclesiastical borders of his mother Church of the East and exercise a profound impact on the development of spirituality first in Byzantium and later in Europe. (The fact that Isaac features in the recent La Théologie byzantine [Turnhout 2015] is indicative). It is not the first time that Kavvadas has addressed Isaac of Nineveh, for he produced a Modern Greek translation of the ‘Second’ part of Isaac's corpus and has authored a number of articles that reveal the decisive influence of Theodore of Mopsuestia.

Kavvadas's study (defended as a doctoral dissertation at Tübingen a few years ago) deals with one of the perennial problems of Christianity, namely the conflict between spiritual authority as contested by an ordained clergy (bishops, in particular) and a holy man whose spiritual power is a gift granted from God. Throughout the history of the Christian Church the relationship between the two poles of authority has often become a matter of conflict. Whereas the subject is well studied in the case of Europe and Byzantium, the material preserved pertaining to the different traditions of the Christian Orient has yet to be properly explored.

The author argues that at the heart of the conflict between the institutional Church of the East (patriarchs, monasteries and schools) and representatives of the mystical movement of the seventh and eighth centuries lies the very same issue regarding spiritual authority. In the words of Kavvadas, ‘They [the mystical authors] considered themselves as representatives of the spiritual stage of Christian existence that lies above the spiritual nature of the Church’ (p. 49). Although the climax of the conflict came at the end of the eighth century, some passages in the works and life of Isaac of Nineveh suggest that he had had to face a very similar attitude. According to Kavvadas's assumptions, theology is dialectically intertwined with history and can be seem fruitfully not only as its reflection but as forming a background for historical events and future developments.

Kavvadas masterfully reconstructs the historical conflict (chapter i) and the soteriological doctrine of Isaac of Nineveh that has much in common with ideas of other monastic authors of that period (chapter ii). The work relies on a close reading of the Syriac (some still unedited) and Greek sources. The Kephalaia gnostika, written in the form of short maxims after those of Evagrius Ponticus, being the most mature of Isaac's compositions, occupies the central position in the author's argument, but Kavvadas does not fail to put to use Isaac's other works. It will suffice here to summarise the content of both chapters.

Such seventh- and eighth-century hermits and authors of mystical works as Isaac of Nineveh, Dadishoʿ Qaṭraya, Shemʿon d-Ṭaybuteh, John of Dalyatha and Joseph Ḥazzaya, whose writings have come down to us, belong to a single spiritual tradition that came into conflict with the institutional Church on a number of issues. These include spiritual interpretation of the Holy Scripture against historical exegesis; mystical knowledge against the Aristotelian-based scholastic of the school movement; freedom of hermits against the canonised ordo of the monasteries; and teaching about divinisation (Vergöttlichungslehre) against reservation on the possibility of reaching complete perfection already in this world. The growing tensions between the two groups became manifest, on the one hand in the accusations of Messalianism against them and an eventual accusation and excommunication by Catholicos Timothy i, and on the other hand in the view of the ‘bearers of the Spirit’ and its supporters that the conflict was due to the envy of the ‘psychics’ (the envy is present in the lives of many East Syriac solitaries).

Experience of the Holy Spirit is the fundamental subject of Isaac's doctrine. All other theological questions (theological knowledge, anthropology, biblical history, hermeneutics of the Scriptures etc.) are approached by Isaac to demonstrate the requirements for the participation in the activity of the Spirit that is capable of granting anticipation of the world to come already in this world.

The value of this book lies in its successful attempt to bring together historical events and theological doctrine. It differs from other studies on Isaac in that it vividly reconstructs the historical and theological context in which Isaac was living and writing. Thus, besides the works of Isaac, the study takes into account many other extant texts issuing out of the East Syriac mystical tradition as well as the sources used by Isaac. Intriguingly, such a critical approach enables us to perceive why Isaac was dealing with certain subjects and even why he pronounced differently on the same issue and why he could disagree with Theodore of Mopsuestia, the Theologian of the Church of the East par excellence. Most importantly, Kavvadas is at pains to demonstrate that despite the unsystematic character of Isaac's teaching, behind his writings stands the clear theological view of an original thinker who masterfully employs the various sources available to him. With that in mind, one can better understand the single manifestations of his thought.

This book is nicely written but requires constant concentration and specialised theological knowledge on the part of the reader, and for that reason can hardly be recommended as undergraduate reading. The author provides on nearly every page original quotations from Isaac in Syriac that are conveniently accompanied by German translations. Some slight imperfections (imprecise transliteration from Syriac, typos, an undeveloped subject index) do not diminish from the overall quality of the work and the author deserves great praise for producing a penetrating study of Isaac of Nineveh that not only represents progress in our knowledge about Isaac and his time but can also be used for a comparison with the Byzantine mystical tradition and Sufism.