The volume is a revised dissertation completed at the Theologische Universiteit Kampen, the Netherlands. Lee's work is prompted by a desire to address the differing paradigms of Trinitarian theology in the East and West and, in recapturing an insight of Théodore de Regnon (+1893) from his later (mis)interpreters, to reveal how their complementarity serves to enrich an understanding of the mystery of God. Much is at stake, Lee rightly notes, for the doctrine of God affects every dimension of the dogmatic and liturgical life of the church.

Lee's study is well organized, and he leads by making clear that the question of the procession of the Spirit is not simply a matter of abstruse metaphysical speculation. He lays out quite clearly and with great care the status quaestionis (26–81) before beginning his comparative study of Gregory and Augustine. He examines carefully both the Faith and Order Commission's “Klingenthal Memorandum” of 1981, as well as the Vatican's Pontifical Council for Promoting Christian Unity document of 1995, which he refers to as the “Clarification.” Both documents pursue a deeper understanding of the relationship between monopatrism and the filioque. Lee's approach takes seriously the real differences between Eastern and Western construals of the procession and hypostasis of the Spirit, with an aim toward genuinely deeper appreciation and understanding of each; in short, his study is marked throughout by an ecumenically sensitive intentionality. More than a mere foray into historical theology, this is a work of scholarship at the service of the churches.

Thus, this study not only offers a comparative study of two pivotal theological giants of East and West, but also serves to orient the reader to the ecclesial implications of the differences of approach and emphasis found in each. After carefully rehearsing Where things Stand, Lee argues that a helpful way forward is by a kind of ressourcement; a (re)turn to Gregory of Nyssa (+395), perhaps the most speculatively gifted among the Cappadocians (81–166), and to Augustine (+430), the most influential of the Fathers on the Western intellectual tradition (167–275). Each of the two is treated individually and at length, with a summary of the Trinitarian thought of each, including their contextual interlocutors, and with particular reference to the epistemological and anthropological categories foundational for their theology, as well as the specific terminology that each employs. The Father's monarchia, the “role” of the Son, and the hypostatic property of the Spirit in the thought each is laid out clearly and with ample textual witness (for Gregory, largely his massive Contra Eunomium; for Augustine, principally his De Trinitate).

Lee concludes that Gregory and Augustine operate with many of the same theological concerns, as they shared a conceptually coherent intellectual universe: the centrality of the distinction between the οἰκονομία / dispensatio and theology proper, as well as of that between ἐνέργεια / operatio and οὐσία / essentia. Both reject any διάστημα / intervallum or “interval,” in God: there is no more or less, beginning or end, before or after, degrees, participations, or gaps. Different contextual worries, however, prompted different emphases: Gregory's concern to demonstrate the deficiencies in Eunomius's epistemology led him to expend considerable effort parsing the relationship between οὐσία and ἐνέργεια, more thoroughly than Augustine was to do. And Augustine's Christological hermeneutic, drawn from Philippians 2, juxtaposing the forma servi and forma Dei, allowed him to develop more thoroughly the Spirit's role as caritas in the progressive healing of the soul and its pivot from temporal to eternal, from scientia to sapientia (206–214). Similarly, in Lee's account, Gregory's use of the language divine φιλανθρωπία functions as the “hermeneutics of the Holy Spirit” in the economy of salvation (153–157), underlining the soteriological coinherence of the missions of Son and Spirit. While, for both, the Father is αἰτία or principium, there is no temporal posteriority or ontological subordination in the generation of the Son or in the procession of the Spirit.

As for the hypostatic property of the Spirit, Lee contends that for Gregory, while the Father is the singular αἰτία of the hypostasis of the Spirit, the Spirit nevertheless proceeds through the Son, whose role is “mediation” (μεσιτεία): “the Spirit proceeds definitively from the Father mediately through the Son, who is the immediate mediation for determining the hypostatic distinction of the Spirit definitively” (291). For Augustine, the Spirit is donum of both Father and Son, and is thus communis to both. Augustine indeed applies the term principium both to Father and to Son, though he further distinguishes the Father as principium principaliter and the Son as principium communiter, so that “the Holy Spirit as being communis to both Father and Son proceeds principaliter from the Father and communiter from the Son” (293). Thus, for both Gregory and Augustine, the Son has an integral role in the procession of the Spirit.

This is an important book, not only for those interested in Trinitarian theology proper, but also for anyone engaged in ecumenical dialogue regarding the filioque. It offers not only a thoughtful introduction to the Trinitarian thought of two theological masters, highlighting their complementarity without sacrificing important nuance, but also reveals the degree to which their Trinitarian metaphysics was crafted with sensitivity and attention to soteriological concerns.