The basis of this Trinitarian theology, which was formulated by the Cappadocian Fathers in the fourth century at the conclusion of the Arian controversies, and which remained standard throughout the Byzantine period, is found in soteriology: the Fathers were actually preoccupied, not with speculation, but with man''s salvation. The Nicaean doctrine of con-substantiality meant «the confession of the fullness of divinity in Christ and implied that the Incarnation was essential to the redemptive act of Christ»; and maintained, similarly, that if «the Spirit is not fully God, He is unable to bestow sanctification» [Both quotations from Georges Florovsky, Vostochnye Ottsy (Paris: YMCA Press, 1931), p. 23]. In itself, the Cappadocian doctrine of the Trinity remains totally meaningless unless one remember that its goal is to maintain the Christological and pneumatological presuppositions developed in the last two chapters: the incarnate Logos and the Holy Spirit are met and experienced first as divine agents of salvation, and only then are they also discovered to be essentially one God. … The doctrine of the three hypostases, adopted by the Cappadocian Fathers to designate the three divine Persons, had definite Plotinian and Origenistic associations, which normally implied substantial differentiation. The Fathers, however, remained faithful to the terminology they had adopted, in spite of all difficulties and criticism …

The Cappadocian Fathers adopted the formulation which would remain the criterion of Orthodox Trinitarian theology in the East: God is one essence in three hypostases. This Cappadocian settlement, given the circumstances of the fourth century, never pretended to be anything more than the best possible description of the divine mystery, not the solution of a philosophical process, similar to the Plotinian «Trinity of hypostases». The Fathers always affirmed that we cannot know what God is, only that He is, because He has revealed Himself in salvation history as Father, Son, and Spirit. God is Trinity, «and this fact can be deduced from no principle nor explained by any sufficient reason for there are neither principles nor causes anterior to the Trinity» [Lossky, Mystical Theology, p. 47].

The same personalistic emphasis appears in the Greek Fathers' insistence on the «monarchy» of the Father. Contrary to the concept which prevailed in the post-Augustinian West and in Latin Scholasticism, Greek theology attributes the origin of hypostatic «subsistence» to the hypostasis of the Father not to the common essence. The Father is the «cause» (aitia) and the «principle» (arche) of the divine nature, which is in the Son and in the Spirit. What is even more striking is the fact that this «monarchy» of the Father is constantly used by the Cappadocian Fathers against those who accuse them of «tritheism»: «God is one», writes Basil, «because the Father is one». [Basil, Ep. 38, 4; PG 32:329CD.] And the same thought is found in Gregory of Nazianzus: «God is the common nature of the three, but the Father is their union [henosis]». [Oratio 42, 15; PG 36:476B.]