From The Christian Doctrine of God, T F Torrance, T & T Clark, London, 1996, pp. 185-186
It has been important to say something in detail of the teaching of Athanasius and Epiphanius, for in pressing further the biblical stress of Athanasius on the ‘I am’ of the one ever-living ever-acting Being of God understood in his internal relations, Epiphanius did more than any other to clear away problems that had arisen in the doctrine of the Trinity and to prepare the ground for the ecumenical consensus that was registered in the Nicene-Constantinopolitan Creed. It was important to throw the spotlight on this development today for it is actually somewhat different from what is found in the usual text book tradition: it was upon the Athanasius-Epiphanius basis that classical Christian theology developed teaching of Gregory Nazianzen who insisted that the Monarchia not be limited to one Person, the doctrinal agreement on the doctrine of the Holy Trinity has been reached between Orthodox and Reformed Churches.1 It is of particular significance for our discussion here that he conception of perichoresis played a crucial role in clarifying and deepening the conception of Monarchia fo the understanding of the interlocking of Unity and Trinity, Trinity and Unity, in the doctrine of God. It may be helpful to cite here a paragraph from a document of the Orthodox/Reformed Commission commenting on the Monarchia in this connection.
Of far reaching importance is the stress laid upon the Monarchy of the Godhead in which all three divine Persons share, for the whole indivisible Being of God belongs to each of them as it belongs to all of them together. This is reinforced by the unique conception of coinherent or perichoretic relations between the different Persons in which they completely contain and interpenetrate one another while remaining what they distinctively are in their otherness as Father, Son and Holy Spirit. God is intrinsically Triune, Trinity in Unity, Unity in Trinity. There are no degrees of deity in the Holy Trinity, as is implied in a distinction between the underived Deity of the Father and the derived Deity of the Son and the Spirit. Any notion of subordination is completely ruled out. The perfect simplicity and indivisibility of god in his Triune Being mean that the Arche (ἀρχή) or Monarchia (μοναρχία) cannot be limited to one Person, as Gregory the Theologian pointed out. While there are inviolable distinctions within the Holy Trinity, this does not detract from the truth that the whole Being of God belongs to all of them as it belongs to each of them, and thus does not detract form the the truth that the Monarchy is One and indivisible, the Trinity in Unity and the Unity in Trinity.2
1. See the memorandum for the proposed dialogue in volume one of Theological Dialogue between Orthodox and Reformed Churches, ed. T F Torrance (Edinburgh, 1985), pp. 3-18; and the Text of ‘Agreed Statement on the Holy Trinity’, in vol. 2. 1993, ch. 7, pp. 219-226.
2. Theological Dialogue between Orthodox and Reformed Churches, vol. 2, ‘Significant features on the Agreed Statement on the Holy Trinity’, the section ‘Trinity in Unity and Unity in Trinity, the one Monarchia’, Trinitarian Perspectives, ch. 9, pp. 137-139.