Perhaps the greatest theological challenge of the early Church was the articulation of the trinitarian identity of the one God. How do we express both the unity and distinctiveness of the divine persons, or as Charles Twombly puts it, their “identity and difference”? It appears to have been easier to identify the heresies. On one side was the Scylla of modalism; on the other the Charybdis of tritheism and subordinationism. Eventually the Nicene Fathers navigated their way through these two perils by taking synonymous philosophical terms, ousia and hypostasis, and creatively reworking their meaning: ousia came to signify the divine essence, and hypostasis the divine persons. Yet something was still missing. The assertion of one essence and three hypostases states the antinomy, but it does not suggest how we might think the two terms together. St John of Damascus found the solution in perichoresis:
The abiding and resting of the Persons in one another is not in such a manner that they coalesce or become confused, but, rather, so that they adhere to one another, for they are without interval between them and inseparable and their mutual indwelling [en allais perichoresin] is without confusion. For the Son is in the Father and the Spirit, and the Spirit is in the Father and the Son, and Father is in the Son and the Spirit, and there is no merging or blending or confusion. And there is one surge and one movement of the three Persons. It is impossible for this to be found in any created nature. (De fid. orth. I.14.11)
John’s assertion of perichoresis (mutual indwelling, coinherence, interpenetration) takes us beyond the fourth century formulations of St Athanasius and the Cappadocians “to a higher level of conceptual refinement by providing a linguistic vehicle that sums up and becomes the condensed expression of a more sophisticated way of relating identity and difference” (Perichoresis and Personhood, p. 9).
Critics of classic trinitarianism will of course argue that perichoresis makes no more sense than the Nicene claim of the consubstantiality of the Father and the Son; but the Damascene would respond that all of our analogies must fail when speaking of the mystery of the transcendent God. The Creator is radically different from the world he has made from out of nothing. The inner life of divinity is not mirrored in the world; hence creaturely parallels to the hypostatic indwelling do not exist. “It is impossible for this to be found in any created nature.” And if they do not exist, then this must mean ultimately mean that the trinitarian unity is, as Twombly remarks, “fundamentally unthinkable” (p. 12).
We dare to think the unthinkable only because the ineffable God has revealed himself in Holy Scripture. “Each hypostasis,” writes Twombly, “is able to reveal because each speaks, as it were, from the inside. And what each reveals … is one or more of the other hypostaseis, though not necessarily the one making the revelation” (p. 14). Only God himself can bridge the chasm between Creator and creature.
For John revelation employs the language of creation (what other language is there?) but uses it both to express truths that the mind unaided would never discover and to point to realities that lie beyond the power of any language to express. As the opening section of the Fount of Knowledge amply shows, John has no hesitancy in “plundering the wealth of Egypt” in his borrowing of philosophical terms and concepts. … But he constantly stretches language to the limits of its conventional usages and strains after that which he believes lies beyond all language. (p. 25)
The theologian does not seek to explain the divine mystery—certainly not in any way that would satisfy philosophers and mathematicians—but simply to state it.
Twombly covers a lot of theological ground in his chapter on the Trinity. Not only does he ably present the teaching of St John Damascene, but he also provides a succinct introduction to the Eastern Christian construal of the Holy Trinity.