The doctrine of deification has become popular – even fashionable – in many scholarly circles, but it is just not evident to most people outside those circles what ‘deification’ actually means. For whatever reason, this doctrine is more evidently in need of explanation than most Christian beliefs. In this volume, Keating attempts to make the meaning of deification available to an educated but non-specialist audience (the book is intended for ‘college, university and seminary courses, as well as […] educated readers of all ages’). Though a considerable knowledge is there in the background, Keating omits many details, in order to provide a concise, informed and illuminating account of a central Christian teaching.

Keating addresses many of the issues that could reasonably be expected to be addressed in an introductory work. Several main convictions shape his exposition.

The first is that, contrary to a stubbornly recurring judgement otherwise, deification (as classically formulated) is grounded in and closely aligned with Scripture. At its simplest deification means that, through the indwelling of the Spirit, God himself comes to live effectively within us. Salvation entails participating in the life of God itself. As Keating shows, the terminology of deification was first employed to describe a specifically biblical understanding of our adoptive sonship in Christ, through the Spirit. Deification was the fruit of the Fathers' efforts to defend and explain the content of Scripture against what they perceived to be its distortions. Chronologically, the much-championed Neoplatonic use of the terminology of divinisation in fact followed Christian usage.

Keating handles the scriptural material deftly and sensitively, paying particular attention to how the Fathers read the scriptures. He draws on recent studies to show how the specifically Jewish context may be even more important than the Graeco-Roman environment for the emergence of the notion of deification. Surprisingly, a short verse from the Greek text of the Old Testament – Psalm 82.6 (‘God stood in the congregation of the gods’) – turns out to have been a primary spur and warrant for the development of the technical terminology, rather than a means of justifying alien conceptions. Contrary to some longstanding assumptions otherwise, another verse – 2 Peter 1. 4 (‘partakers of the divine nature’) – does not seem to have played a significant role in the development of the language of deification.

A second conviction that shapes Keating's work – and one that gives this book its overall structure – is that, if deification is to be understood at all, it must be understood within the creedal confession of the church and within the practice of believers. The doctrine is neither an exotic discovery, nor an alternative path to God. It depends entirely on the specific confession of a Trinitarian God, the Incarnation, and the indwelling Spirit in the Church. In fact, in the Fathers, the language of deification is typically found in contexts where they are defending and explaining the full divinity of the Son and the Spirit (and so, the doctrine of the Trinity).

Keating provides enlightening and stimulating explorations of the historical development of the doctrine. He shows its interrelatedness with the Fathers' sacramental theology and elements of Christian asceticism and prayer. He further demonstrates how deification makes sense of various rich ethical notions: our transformation in the image of Christ, Christian ‘perfection’ or maturity, our share in the suffering and death of Christ.

In his exposition of the historical development, Keating draws widely on Fathers from the West as well as from the East. By this means he gradually reveals the reasonableness of a third conviction (again in line with recent studies). That is, that the doctrine is not the exclusive patrimony of the Eastern Church and just an eccentricity of certain theologians in the West. Perhaps Keating's most notable conclusion is that deification lies at the patristic root of both Eastern and Western theological traditions. Keating shows how the notion did not, in fact, die in the West. Moreover he repeatedly, and without hesitation, moves from quoting the Greek Fathers to quoting Aquinas. He shows that the patristic notion has a lively presence in Aquinas, who not only employs some of the characteristic vocabulary, but – more importantly – expresses and develops its content. Keating also identifies how aspects of deification can be found in key Protestant reformers and theologians (Luther, Calvin, Wesley). At no point does he deny the real differences between Eastern and Western understandings of this teaching, he simply reveals the striking similarities on essentials.

A concise account of this kind necessarily leaves out many things (as Keating is well aware). Unsurprisingly, he scarcely touches a series of thorny questions about grace (although the word does figure in his title, oddly). A particular difficulty with treating deification systematically, as though it were a single doctrine, is that this tends to flatten differences in terminology and understanding between different authors. This is a pity, because a good deal can be learnt – both about the author and the tradition – by observing which strand of the tradition a given author grasps and which he neglects. On occasion, Keating might have done more at least to register the differences in language between the authors he quotes.

On the other hand, Keating had to choose among his difficulties, and it is hard not to feel that he chose wisely in his basic options. More specialist books deal with what is deliberately omitted here (see, for instance, Norman Russell's work). At the end of the day, it is a relief to find a book written by a very competent scholar that addresses people who are less than competent scholars, in a way that is both engaging and enriching. Such books are needed to help reveal to the non-specialist how and why the classic shape of Christian thought provides the most satisfying interpretation of the Bible. They are also and especially needed to puncture silly or trivial caricatures of Christian talk about God and faith. It is to be hoped that, in writing for this audience, Keating will help to bring this understanding just a bit further into the marketplace.