The Leitsatz (thesis statement) for §9 states: "The God who reveals Himself according to Scripture is One in three distinctive modes of being subsisting in their mutual relations : Father, Son, and Holy Spirit. It is thus that He is the Lord, i.e., the Thou who meets man’s I and unites Himself to this I as the indissoluble Subject and thereby and therein reveals Himself to him as his God."
In subsection §9.1 ("Unity in Trinity"), Barth begins his discussion of the Trinity with a brief comment about how the triunity of God is to be conceived. Barth insists that the affirmation of the doctrine of the Trinty in no way abrogates the confession that God is One. In no way does the divine Trinity conflict with the divine unity:
The doctrine of the triunity of God, as this has been worked out and lightly maintained in the Church as an interpretation of biblical revelation regarding the question of the Subject of this revelation, does not entail—this above all must be emphasised and established—any abrogation or even questioning but rather the final and decisive confirmation of the insight that God is One.Barth emphasizes this unity in a number of ways - not the least of which is the trinitarian baptismal formula used so widely in the Church. It is not in the names of the Father, Son, and Holy Spirit - but in the name of the Father, Son, and Holy Spirit by which Christians are initiated. What could this mean but that there is One God:
The concept of the unity of God as such will claim our attention later in the doctrine of God. It concerns us here only in relation to the further insight that God’s triunity does not imply any threat to but is rather the basis of the Christian concept of the unity of God (348).
The trinitarian baptismal formula could not be more wrongly understood than by understanding it as a formula of baptism into three divine names.
The faith which is confessed in this formula, and similarly the faith of the great three-membered confessions of the ancient Church, is not, then, a faith which has three objects.
Three objects of faith would mean three gods. But the so-called “persons” in God are in no sense three gods (349).This reflects that the faith of the Church does not have three objects, which would mean three gods, but One.
We may unhesitatingly equate the lordship of God, to which we found the whole of the biblical concept to be related, with what the vocabulary of the early Church calls the essence of God, the deitas or divinitas, the divine οὐσία, essentia, natura, or substantia. The essence of God is the being of God as divine being. The essence of God is the Godhead of God.
It may be said of this essence of God that its unity is not only not abrogated by the threeness of the “persons” but rather that its unity consists in the threeness of the “persons.” Whatever else we may have to say about this threeness, in no case can it denote a threeness of essence. The triunity of God does not mean threefold deity either in the sense of a plurality of Gods or in the sense of the existence of a plurality of individuals or parts within the one Godhead (349-350).The Church doctrine of Trinity can be summed in the phrase God is Trinity, such that what the trinity implies is that God is the one Lord in threefold repetition.
The name of Father, Son and Spirit means that God is the one God in threefold repetition, and this in such a way that the repetition itself is grounded in His Godhead, so that it implies no alteration in His Godhead, and yet in such a way also that He is the one God only in this repetition, so that His one Godhead stands or falls with the fact that He is God in this repetition, but for that very reason He is the one God in each repetition (350).Barth rejects the idea of God as a generic or "collective" unity - rather he emphasizes the numerical unity of the essence of the "persons." "Person" here is a threefold repetition of God - not a unique species, as if Father, Son, and Holy Spirit were unique personalities in themselves. Each repetition is grounded in the One Godhead, and God is God only in this repetition:
“Person” as used in the Church doctrine of the Trinity bears no direct relation to personality. The meaning of the doctrine is not, then, that there are three personalities in God. This would be the worst and most extreme expression of tritheism, against which we must be on guard at this stage. The doctrine of the personality of God is, of course, connected with that of the Trinity to the extent that, in a way yet to be shown, the trinitarian repetitions of the knowledge of the lordship of God radically prevent the divine He, or rather Thou, from becoming in any respect an It. But in it we are speaking not of three divine I’s, but thrice of the one divine I. The concept of equality of essence or substance (ὁμοουσία, consubstantialitas) in the Father, Son and Spirit is thus at every point to be understood also and primarily in the sense of identity of substance. Identity of substance implies the equality of substance of “the persons” (351).Barth reminds us that the unity of the Trinity is given to us in revelation, such that we don't have to choose between the unity of the Godhead and revelation. This is not the case with the various monarchial heresies (outlined in detail on pg. 352f.), which force one to choose between revelation and unity.
Inevitably—and we must see this if we are to understand the sharpness with which the Church has fought it—all antitrinitarianism is forced into the dilemma of denying either the revelation of God or the unity of God. To the degree that it maintains the unity of God it has to call revelation in question as the act of the real presence of the real God. The unity of God in which there are no distinct persons makes it impossible for it to take revelation seriously as God’s authentic presence when it is so manifestly different from the invisible God who is Spirit. On the other hand—and this must be our primary concern here—to the degree that it is ready to maintain revelation but without acknowledging the substantial equality of the Son and the Spirit with the Father in heaven, the unity of God is called in question. In its concept of revelation it will not in fact be able to avoid interposing between God and man a third thing which is not God, a hypostasis which is not divine—it does not want that—but semi-divine; it cannot avoid making this the object of faith. In so far as it is not a denial of revelation, antitrinitarianism in any form is a cruder or subtler deifying of revelation (352).What we receive in revelation is the knowledge that subject, predicate, and object are the same as revealer, revelation, and revealing - the God who is both YHWH and LORD is a unity in trinity - one in which Father, Son, and Holy Spirit are equal.
If revelation is to be taken seriously as God’s presence, if there is to be a valid belief in revelation, then in no sense can Christ and the Spirit be subordinate hypostases. In the predicate and object of the concept revelation we must again have, and to no less a degree, the subject itself. Revelation and revealing must be equal to the revealer. Otherwise there is no room for them beside the revealer if this be the one God. The unity of God would render revelation and revealing impossible. Christ and the Spirit would not just be foreign to and totally unlike the Father, as Arius said in dangerous proximity to a denial of all revelation. They would have no more to do with Him than any other creatures. Only the substantial equality of Christ and the Spirit with the Father is compatible with monotheism (353).
