Katherine Sonderegger identifies Karl Rahner and Karl Barth, respectively, as the seminal heads who initiated what has been called the Trinitarian Revival. She writes:
The “Trinitarian Revival” has been traced to twin geniuses: Karl Rahner and Karl Barth. Rahner’s remarkable essay for his encyclopedia, Mysterium Salutis, now published separately as The Trinity. Joseph Donceel, trans. New York: Herder, 1970. (New York: Crossroad, 2003) provides the template for considering much Christian piety as “sheer monotheism”—see p. 42, note 43. Karl Barth announced the Trinity as a form of revelation in his Church Dogmatics, I.1, thereby joining the modern doctrine of revelation to the Triune God as proper and sole Subject of dogmatics. Because of the Christological concentration of these doctrines of the Trinity, they remain distinctly modern, belonging to the pronounced Christological focus of modern theology, and not simply as variants on Peter Lombard’s Sentences and early Trinitarianism in the doctrine of God.
Ultimately Sonderegger does not think this style of “revival” has been a good thing; the above quote is a footnote she wrote tied to commentary she was offering on the impact that modern theology, a la Barth et al., has had upon the shape of Trinitarian theology. She sees the emphasis upon the threeness of God (de Deo trino), promoted by Barth, Rahner, et al., as something that has had a negative impact upon understanding God as One (de Deo uno). Sonderegger writes:
Once more we must pause before a seemingly anodyne, wholly biblical phrase: the One God. Perhaps nothing so marks out the modern in systematic theology as the aversion to the scholastic treatise, De Deo Uno. It belongs not to the preface but rather the body of the dogmatic work to lay out the broad movement in present day dogmatics that has pressed the treatise De Deo Trino to the fore; indeed, it crowds out and supplants the exposition of the One God. But even here we must say that the doctrine of the Trinity, however central to the Christian mystery, must not be allowed to replace or silence the Oneness of God. God is supremely, gloriously One; surpassingly, uniquely One. Nothing is more fundamental to the Reality of God that [sic] this utter Unicity. Such is God’s Nature; such His Person: One. Oneness governs the Divine Perfections: all in the doctrine of God must serve, set forth, and conform to the transcendent Unity of God. Now, to say all this aligns the Christian doctrine of God with the faiths of Abraham, Judaism, and Islam; indeed of all monotheisms—for monotheism is not a shame word! The Christian affirmation of divine Unicity opens it, like the merciful and welcoming Lord it serves, to the peoples and faiths of the good earth. But this cannot serve as ground for such a fundamental axiom in dogmatics. Rather, we must appeal to Holy Scripture.
She clearly has a problem with the modern turn in what has now come to be called Trinitarian theology (ironically because of the modern turn). It appears, though, that she is over-correcting by so emphasizing the Oneness of God that she already is starting to lose sight of how the Oneness is oneness by almost denigrating the Threeness of God; which would be ironic because ever since at least the councils of Nicaea and Constantinople the threeness and oneness of God have been inextricably linked within the Christian grammar.
But as we recall in the footnote I shared from her, she does mention Peter Lombard’s Sentences. This might clue us into the turn-back she is attempting to make, and how she thinks a doctrine of God should develop. It says much about her theory of revelation; she’s obviously not a Barthian (or potentially not even an Athanasian). Like Lombard she is going to want to follow the progressive unfolding of Scripture in salvation history. As such she opens to the Torah, the first five books of the Bible, and works her way, in a seemingly linear fashion, from there until she gets to Jesus. Once she gets to Jesus in the New Testament she will start reflecting on the threeness of God. Sonderegger is actually following not only Lombard’s lead, but the lead found in the scholastic developments of theology embedded in Post Reformed orthodoxy.
I once wrote about how the scholastics Reformed placed a rupture between the Oneness of God and the Threeness. Here’s what I wrote as I had just finished comparing how a doctrine of God is developed in various Reformed confessions, and a chatechism:
At first blush there might not be much apparent difference between TheWestminster Confession of Faith (WCF), The Belgic Confession of the Faith (BC), The Heidelberg Catechism (HC) and The Scott’s Confession 1560 (SC); but this requires further reflection. The “Westminster” tradition starts talking about God by highlighting his “attributes,” these are characteristics that are contrasted with what humans are not (analogia entis). We finally make it to God as “Father, Son, Holy Spirit,” but not before we have qualified him through “our” categories using humanity and nature (analogia entis) as our mode of thinking about “godness.” This is true for both the WCF and the BC. Jan Rohls provides a helpful insight on this when he speaks to the nature of the composition of many of the Reformed Confessions (including both the WCF and the BC):
It is characteristic of most of the confessional writings that they begin with a general doctrine of God’s essence and properties, and only then proceed to the doctrine of the Trinity. The two pieces “On the One God” (De deo uno) and “On the Triune God” (De deo trino) are thus separated from each other. . . .
We now see this move being made in Sonderegger’s work. It’s not a new thing then, but a call back to the calmer waters, as Sonderegger might see it, of classical theism; and away from the turbulent seas that modern theology has presented the church with.
Should we be afraid of speaking of God’s Oneness and Threeness in the same breath? Was the ancient church afraid of doing so? I don’t think so. Thomas Torrance, who I also once quoted has this to say about this type of move by Sonderegger:
. . . in the Scots Confession as in John Knox’s Genevan Liturgy, the doctrine of the Trinity is not added on to a prior conception of God—there is no other content but the Father, the Son, and the Holy Spirit. There was no separation here between the doctrine of the One God (De Deo Uno), and the doctrine of the triune God (De Deo Trino), which had become Roman orthodoxy through the definitive formalisation of Thomas Aquinas. This trinitarian approach was in line with The Little Catechism which Knox brought back from Geneva for the instruction of children in the Kirk. “I believe in God the Father, and in Jesus Christ his Son and in the Holy Spirit, and look for salvation by no other means.” Within this trinitarian frame the centre of focus in the Confession and Catechism alike is upon Jesus Christ himself, for it is only through him and the Gospel he proclaimed that God’s triune reality is made known, but attention is also given to the Holy Spirit. Here once again we have a different starting point from other Reformation Confessions. Whereas they have a believing anthropocentric starting point, such as in the Heidelberg Catechism, this is quite strongly theocentric and trinitarian. Even in Calvin’s Institute, which follows the fourfold pattern in Peter Lombard’s Sentences, the doctrine of the Trinity is given in the thirteenth chapter within the section on the doctrine of God the Creator. Calvin’s Genevan Catechism, however, understandably followed the order of the Apostles’ Creed. The trinitarian teaching in the Scots Confession was by no means limited to the first article for it is found throughout woven into the doctrinal content of subsequent articles.
Sonderegger would most likely respond that Torrance is simply a modern theologian himself; following in the steps of Barth and Rahner working out the so called “Trinitarian Revival.” But I think she’s wrong. I think Torrance’s insight, as well as the facts on the ground, blunts her critique of the modern trajectory within Trinitarian theology. Sure, yes, modern theology has flavored Trinitarian theology a certain way (i.e. in almost anti-metaphysical ways, which is what I think Sonderegger is really troubled by), but I don’t think the allergy of speaking of God’s Oneness and Threeness together is as present say in Pro-Nicene theology as she seems to want to make it.
I’ll leave you to decide …
 Katherine Sonderegger, Systematic Theology. Volume 1 Doctrine of God (Minneapolis: Fortress Press, 2015), xxiii, n. 4.
 Ibid., xiv.
 Bobby Grow, “Analogia Fidei or Analogia Entis: Either Through Christ or Through Nature,” in eds. Myk Habets and Bobby Grow, Evangelical Calvinism: Essays Resourcing the Continuing Reformation of the Church (Eugene, OR: Pickwick Publications, 2012), 108.
 Thomas F. Torrance, Scottish Theology cited Ibid., 110.