At the time of the Renaissance, the mystical tradition, as demonstrated in the fourth chapter, takes on a strong esoteric colouring. The Hermetic Corpus and the central texts of the Kabbalah, translated into Latin and understood as pagan and Jewish prefigurings repectively of the coming of Christ, become authoritative teachings, which, although ultimately marginalised, feed through Jakob Boehme and others into modern Orthodox thinking on theosis.

The first chapter explores the meaning of religion - which is much broader than the belief-system of any given ecclesial communion - and also the meaning of theosis in its early historical development. Religion is considered up to the early modern age but theosis only to the end of the patristic age as the springboard for the study of later developments as they relate to religion.

The final chapter examines the re-engagement of Western academics with theosis in the twenty-first century and explores how, through such publications as the Philokalia and The Way of a Pilgrim, the notion of theosis has reached a broad non-churchy audience.

In the fifth chapter it is shown how the esoteric feeds into the Russian sophianic version of theosis, as expressed by Soloviev, Florensky, and the early Bulgakov, through the spirituality of the Philokalia in its Slavonic and Russian versions and the thinking of Boehme, Steiner, and others, while at the same time the patristic teaching on deification is retrieved through the important work of Ivan Popov.

The second chapter traces the post-patristic career of theosis in the Byzantine world from its role in the promotion of Chalcedonian Christology in the sixth century through to the definition (at the Constantinopolitan Council of 1351) of theosis as participation in the uncreated energies. A postscript explains why the Byzantine tradition was taken up in modern times not by the Greeks but by the Russians.

The Afterword summarises the previous seven chapters, arguing that theosis is not a gnostic type of spiritualisation that de-creates us but the bringing of creation as a whole to its ultimate fulfilment.

The sixth chapter examines the patristic revivals of theosis in the early twentieth century by the Russian émigré theologians of the ’Paris School’, principally through the work of Myrrha Lot-Borodine, Vladimir Lossky, and the later Bulgakov. The first two of these writers engage with modern theologians partly to differentiate Orthodoxy from its new Catholic environment and partly (especially in Lossky’s case) to enable Western theology to enrich itself through interacting with Orthodox thinking.

The third chapter looks at the Western reception of Dionysius the Areopagite in the early Middle Ages and the channelling of thinking on theosis through Dionysius into the Western mystical tradition. This tradition is examined from Bernard and Bonaventure to the Rhineland mystics and Nicholas of Cusa, revealing a constant concern to integrate the intellectual ascent to the vision of God with experiential participation in the Word by faith.

The Introduction surveys the different meanings of theosis and religion that have evolved over the centuries as a way of defining the book’s principal terms. Then after discussing the recent debate about whether theosis is a doctrine or a theological theme, it introduces the subsequent chapters as an exercise in intellectual history. The narrative thread of this history is provided by the different receptions of Dionysius the Areopagite in Eastern and Western Christianity. Theosis emerges as a polyseme, its meaning defined by the different contexts in which it is used.