Previously, we have asked and discussed how the Father, the Son, and the Holy Spirit are One, that there is truly One in Three. Now, the opposite and complement question would be: How could we express the distinction in the essence of God within this unity? How could there really be Three in One? The Western tradition expressed it using the term of persona while the Eastern tradition expressed it using the term of hypostasis (Indonesians followed the Western tradition as pribadi, as in private, is closer to persona — it can be extended as well to become kepribadian which corresponds with personalitas). Barth then argued that he preferred “modes of being” (Seinsweisen) rather than “person”, as he thought that it was very difficult to argue what is really meant by “person” without being prone too much into tritheism. It must be quicky noted, though, that “way of being” was translated from the German word Seinsweise, of which the translators have noted the difficulty in translating this word (I/1, viii). And, the translators have noted that this translation might be prone or hint modalism or Sabellianism. By all means, what Barth intended was to refer back to the Cappadocian tropos hyparxeos or to the Protestant modus entitativus (and I don’t know how each of them used these terms, respectively). Hence, there is a distinction of God’s mode of being as the Father, God’s mode of being as the Son, and God’s mode of being as the Spirit, although each mode of being is of course is not independent to each other but rather subsists in the other two.
To put it in a perhaps more human way (to describe the inner life of God!), the unity of God is inherently intra-relational. The Father exists eternally as the Father from whom the Son is eternally begotten, the Son exists eternally as the Son who is begotten eternally by the Father, and, finally, the Spirit exists eternally as the Spirit who proceeds from the Father and the Son (yea, Barth followed the Western tradition). I’m going to summon the spirit of Rowan Williams here. The problem with Arius is he tried to solve the mystery of the Father begetting the Son by saying that there must be a time where the Son was not. The counter argument would be, in that case, the Father started to become the Father only after he beget the Son. There was a time where the Father was not the Father, then. No. The Father is the Father because he is, by his distinctive mode of being, the Father. Hence, the Father is the Father because he eternally begets the Son, and likewise, the Son is the Son because he is eternally begotten by the Father. Thus the title of Eberhard Jüngel’s book, God’s Being is in Becoming: The Trinitarian Being of God in the Theology of Karl Barth. God’s being is in his becoming.
If you started to scratch your head, don’t worry, as you are clearly not alone. In the end of this subsection on the Trinity in unity, Barth confessed that in the end “[w]e, too, are unable to say how in this case 3 can really be 1 and 1 can really be 3.” (367) That, in the end, “the mysterium trinitatis remains a mystery.” (367) I’ll close with a longer quote: “Theology means rational wrestling with the mystery. But all rational wrestling with this mystery, the more serious it is, can lead only to it fresh and authentic interpretation and manifestation as a mystery. For this reason it is worth our while to engage in this rational wrestling with it. If we are not prepared for this we shall not even know what we are saying when we say that what is at issue here is God’s mystery.” (367)
Additional thought: Note that, if I understood him correctly, Barth followed the Western tradition, that tried to explicate the Trinity on the basis of the unity of God. On the other hand, from what I heard (since I’ve never really read the primary sources), the Eastern tradition based it on the Fatherhood of the Father — and hence the difference of the filioque and so on.