The Incarnation, the point of departure for theology, immediately puts at the heart of the latter the mystery of the Trinity. He Who is incarnated is indeed none other than the Word, that is to say, the second person of the Trinity. Incarnation and Trinity are thus inseparable, and against a certain Protestant criticism, against a liberalism which would oppose Gospel and theology, we must stress the evangelical roots of the orthodox triadology. Can one indeed read the Gospel without asking the question: who is Jesus? And when we hear the confession of Peter: “Thou art the Son of the living God” (Matt. 16:16), when St. John opens to us eternity with his Gospel, we understand that the only possible answer is the dogma of the Trinity, the Christ, only Son of the Father, God equal to the Father, identical divinity and different person.

The chief source of our knowledge of the Trinity is, indeed, none other than the Prologue of St. John (and also the first epistle of the same), and that is why the author of these amazing texts has received, in the Orthodox tradition the name of St. John the Theologian. From the first verse of the Prologue, the Father is called God, Christ is called the Word — and the Word, in this beginning which is here not temporal but ontological, is at once God (“in the beginning ... the Word was God”) and other than the Father (“and the Word was with God”). These three affirmations of St. John: “In the beginning was the Word — and the Word was with God — and the Word was God,” constitute the germ of all trinitarian theology. They immediately direct our thought to the obligation of affirming, at the same time, the identity and the diversity of God.

Certainly it is tempting to shatter the antinomy by rationalizing one or the other of its terms. Thus there have appeared, more or less explicitly, two major heretical tendencies: Unitarianism and Tritheism.

Unitarianism has often assumed the aspect of an absolute monarchianism: there is only one person in God, that of the Father, Whose Son and Spirit are only emanations or forces. Its most perfect expression was in the third century, the modalism of Sabellius, where the very notion of person-hood disappeared. For Sabeliius indeed, God is an impersonal essence which manifests itself diversely to the universe. The three persons are then no longer anything but three successive modes of action, three appearances to the world of the same monad always simple in itself. Through creation God takes on the shape of Father. The Father is thus the aspect of a first phase of divine manifestation linked with the genesis and the paradisiacal state. But sin modified the relation between God and man; the era of the Father finished and God took another aspect, that of the Son, whose complete manifestation corresponded to the Incarnation. With the Ascension, the filial mode of divinity was once more absorbed into the essential mdistinction and a new mode appeared, that of the Spirit. At the Final Judgement, when the universe will be divinized, everything will enter into the indivisible monad. This successive Trinity remains thus a pure appearance and in no way concerns the reality itself of God: here, nature completely absorbs the persons.

The opposite heresy, pure Tritheism, has never been expressed. But if the absurdity of a divergent Trinity cannot be formulated, one often observes a certain weakening of the trinitarian reciprocity: a Trinity without equality and finally relinquished. Before Nicaea subordinationistic tendencies were powerful in Christian thought, particularly with Origen. Under the influence of Neo-Platonism, the Father was identified with supreme unity, so that one could not thereafter distinguished the Son except by subordinating Him. Divinity did not properly belong to Him; He only participated in the divine nature of the Father. The Logos thus became the instrument of the One, and the Holy Spirit in its turn served as an instrument for the Son with which to sanctify on behalf of the Father.

With Arius this tendency became a heresy which broke the trinitarian unity. Arius identified God and the Father, and claimed that all which is not God is created. The Son is therefore created, since He is other than the Father, and the personal difference results in an ontological break. This created Son creates in His turn the Spirit, and the Trinity reverts to a hierarchy where the inferior serves as instrument to the superior, and which is shot clean through by that insuperable gap which separates the created from the uncreated. Generation becomes creation, the Son and the Spirit, “grandsons,” who are creatures radically distinct from paternal divinity, and the triad only survives by dividing the monad.

By contrast, faith, jealously preserved by the Church, seizes in a single movement, with a single adhesion, the unity and the diversity of God. But our intelligence must also be religious, and it is not only feeling, but also thought, which must open itself to the truth, or rather neither of tbem separately but our whole being, at once fervent and lucid. The triumph of Christian thought is to have elaborated over the first four centuries, and particularly during the fourth, “trinitarian” par excellence, a definition which gave to the heathen an inkling of the fullness of the Trinity: this was not the rationalization of Christianity but the Christianization of reason, a transmuting of philosophy into contemplation, a saturation of thought by a mystery which is not a secret to conceal, but an inexhaustible light. This grand work, over which Athanasius of Alexandria, Basil, Gregory of Nyssa and Gregory of Nazianzus, and also Hilary of Poitiers, all collaborated, finally enabled the Church to express, by the term ομοουσιοζ, the mystery of the divinity at once monad and triad. Oμοουσιοζ means consubstantial, identical in essence, co-essential; this is the adjective which qualifies the Son, God and other than “the God,” the same but not the Father.

“The Word was with God” says the Prologue of St. John: προζ τον Θεόν. Προζ denotes movement, a dynamic closeness: one could translate it as “towards” rather than “with”: “The Word was towards God.” Προζ thus includes the idea of a relationship: this relationship between the Father and the Son is eternal generation, and we are thus introduced, by the Gospel itself, to the life of the divine persons of the Trinity.

It is also the Gospel that reveals to us the trinitarian “location” of the Holy Spirit, and the relations which stress Its own personal uniqueness. It is enough to read in St. John the last words of the Lord to the Apostles: “And I will pray to the Father to send you another Comforter (Protector) to be with you always: … the Spirit of Truth”(14:16–17) and again: “The Protector, the Holy Spirit Whom the Father will send in my Name” (15:26). The Spirit is then other than the Son, Who is also a Comforter, but He, the Spirit, is sent in the name of the Son to bear witness to Him. His relation to the Son is then neither one of opposition nor of separation, but of diversity and reciprocity — thus, of communion in the Father.

It is the same for the relation of the Spirit to the Father: “The Spirit of Truth which proceeds from the Father” (15:26): the Spirit is different from the Father, but united to Him by a bond of procession which is proper to Him and differs from the generation of the Son.

The Son and the Spirit thus appear, throughout the Gospel, as two divine persons sent into the world, the former to quicken our personal liberty, the latter to unite Itself with our nature and regenerate it. These two persons each have their proper relation to the Father (generation and procession); they also have between them a relationship of reciprocity: it is thanks to the purification of the Virgin by the Spirit that the Son could be given to men, as it is by the prayer of the Son ascended back to the right hand of the Father that the Spirit is dispensed to them (“the Protector Whom I will send you from the Father,” John 15:26). And these two persons appear, in the eternity which unfolds, equal in dignity to the Father and identical to Him in substance. They transcend the world where they act: the one and the other are indeed “with” the Father, Who does not Himself come into the world, and their closeness to the Father, source of the divine nature, manages to locate for our thought the Trinity in its transcendence, its stability and its fullness.