When in the realm of Barth studies, you will often hear of ‘Barth’s actualism.’ But what in fact is actualism in Barth’s theology? And might it, once understood, offer the way out of the classical modes of thought in regard to God’s relation to the world through the decretum absolutum (‘absolute decree’)? In other words, could Barth’s actualism allow us to 
understand God’s ways vis-à-vis the world in such a way that God is no longer understood to be a static monad, but instead, a relational and personalist God, who indeed is constituted by his perichoretic co-inhering relations as Father, Son, and Holy Spirit?
George Hunsinger writes the following in an attempt to capture the entailments of Barth’s deployment of a what might be called a ‘trinitarian actualism’:
“Actualism” is the motif which governs Barth’s complex conception of being and time. Being is always an event and often an act (always an act whenever an agent capable of decision is concerned). The relationship between divine being and human being is one of the most vexed topics in Barth interpretation, and one on which the essay at hand hopes to shed some light. For now let it simply be said, however cryptically, that the possibility for the human creature to act faithfully in relation to the divine creator is thought to rest entirely in the divine act, and therefore continually befalls the human creature as a miracle to be sought ever anew.[1]
This is helpful, as far as it goes, but I think this requires further elaboration. Travis McMaken, with reference to the aforementioned work of Hunsinger, refers us to Hunsinger’s description of Barth’s actualism thusly:
. . . Although precisely what to make of Barth’s actualism has become something of a contested point in contemporary anglophone Barth studies, Hunsinger’s orienting discussion remains a helpful starting point: actualism is in play “in the language of occurrence, happening, event, history of decisions, and act. At the most general level it means that [Barth] thinks primarily in terms of events and relationships rather than monadic or self-contained substances. So pervasive is this motif that Barth’s whole theology might well be described as a theology of active relations.”[2]
So, for Barth, according to Hunsinger, actualism is focused on God’s initiative for the world in such a way that God includes the world in his initiative insofar that that is circumscribed by his free determination to be with the world in Jesus Christ. The focus is on God’s ‘being-in-becoming,’ with an emphasis on God’s being as determinative of his becoming, and as such the world’s existence in that becoming as that is actualized in the Logos ensarkos (the Word made flesh). It is because of this triune and personalist determination that the emphasis, in Barth’s theology, is on event and narratival history, as that is deposited for us in Holy Scripture. But to be sure, it is God’s being-in-becoming, and thus trinitarian actualism, that is indeed the history that is, we might say, the historizing history by which history comes to have the capacity to bear witness to its reality in Jesus Christ.
We might be in a better position now to understand how Barth’s actualism offers an alternative way to conceive of a God-world relation that indeed can be grounded in a dogged focus on the text of Holy Scripture (rather than the speculations of the philosopher-theologians as they think God from an actus purus or ‘pure being’ theology). For Barth, actualism entails that our knowledge of God is exhaustively predicated by God’s election to be for us in Jesus Christ. It is this event alone that grounds all of our knowledge of God, and yet also protects us from the temptation of imagining that we, indeed, might be able to imagine, and thus ‘possess’, who God is as that takes formation through a speculative process of abstract intellection and tradition-building.
As Hunsinger leaves off, “For now let it simply be said, however cryptically, that the possibility for the human creature to act faithfully in relation to the divine creator is thought to rest entirely in the divine act, and therefore continually befalls the human creature as a miracle to be sought ever anew.”[3] For Barth, and I would suggest, for the most fruitful Protestant way, it is best to think of a God-world relation as a ‘miracle’; that is, as the predicate of the sui generis reality, and analogy of the incarnation of God. This is not something that we bring to God, but what God has actualized for us based on his freedom to be for, in, and with us in Christ. This is not a static, nor thus, a monadic thing, but remains a dynamic, organic, and relational reality insofar that God himself is the same yesterday, today, and forever. As such, actualism for Barth entails that it is God’s continuous ‘event-nature’ whereby the Christian existence is refreshed and renewed, moment-by-moment, as we seek Him first, His kingdom and His righteousness. He blows into our lives by the fresh breath of the Holy Spirit, and encounters us, that we might encounter him; and by such encounter, come into the plenitude of God’s effervescent life of koinonial affection as Father, Son, and Holy Spirit. But it is this actualism that ensures that it is God we are encountering afresh and anew, and not merely projections of our own imaginative efforts in regard to who we might hope God might be (along with the philosophers).
[1] George Hunsinger, How To Read Karl Barth: The Shape of His Theology (New York/Oxford: Oxford University Press, 1991), 16-18.
[2] See W. Travis McMaken, The Sign of the Gospel: Toward an Evangelical Doctrine of Infant Baptism after Karl Barth (Minneapolis: Fortress Press, 2013), fn. 54 loc. 4695, 4698 citing Hunsinger, How to Read Karl Barth, 30.
[3] Hunsinger, How to Read Karl Barth, 16.