One of the first hooks for me with Barth’s theology was his conception of what is called the analogia fidei (‘analogy of faith’ — in contrast to the classical analogia entis ‘analogy of being’). At first reading and contemplation I thought it was a better way because I was already predisposed against the mechanical universe of classical theism; and the inter-chained hierarchy of being that held it together (think of Thomas Aquinas’s theology and substance metaphysics). In other words, if there was not necessary symmetry (albeit analogically understood and thus asymmetrical at certain levels i.e. Creator/creature) between God and all subsequent contingent reality then how might we as creatures gain a knowledge of God devoid of this type of interrelation between ‘being?’ I didn’t have an articulated sense of this dilemma, maybe just an inchoate unacknowledged sense; but one that came from my working in the area of historical theology with the realization that even in late medieval theology under the impact of the nominalists this ‘chain-of-being’ idea had already been critiqued and found wanting (at least for some). No matter the influence, what I found in Barth’s theology in regard to a theological epistemology (and ontology) resonated and resonates with me deeply. In order to expose you to what I am referring to I am going to transcribe a long quote from Bruce McCormack where he describes the Göttingen Barth’s understanding of knowledge of God. What you will see is that Barth, as a modern, was responding to and working from Kantian categories; nevertheless, what you will also see in McCormack’s development, is that Barth reified and in fact flipped Kant’s categories on their head insofar as the ‘knowing subject’ is not you and me, but instead Jesus Christ for us.
At the heart of Karl Barth’s doctrine of revelation, in the form in which it was first given a relatively full and positive elaboration in the Göttingen lectures on dogmatics, lies the concept of “indirect identity”: in revealing himself God makes himself to be indirectly identical with a creaturely medium of that revelation. Such a relation is indirect because the use made by God of the creaturely medium entails no “divinisation” of it. The veil in and through which God unveils himself remains a veil. And yet it must also be said that in the act of Self-revelation, God is indirectly identical with the creaturely medium. That is to say, the presence of God in the medium of revelation—however hidden it may be outwardly, to normal perception—is the presence of God, complete, whole and entire (without division or diminution). The hiddenness of God in revelation is not to be likened to the hiddenness of the submerged portion of an iceberg. It is not as though part of God is revealed directly while part of God remains hidden to view. No, Barth makes it quite clear that if revelation is Self-revelation (and it is), then revelation means the revelation of God in his entirety—but the whole being of God hidden in a creaturely veil. Nothing of God is known directly; God remains altogether hidden. And yet, where God is truly known in his hiddenness, it is the whole of God which is known and not “part” of God.
Expressed christologically: the process by means of which God takes on human nature and becomes the Subject of a human life in our history entails no impartation of divine attributes or perfections to that human nature. And therefore revelation is not made to be a predicate of the human nature of Jesus; revelation may not be read directly “off the face of Jesus.” And yet it remains true that God (complete, whole, and entire) is the Subject of this human life. God, without ceasing to be God, becomes human and lives a human life, suffers, and dies.
The principle consequence of this conception of an indirect revelation for theological epistemology is that God is the Subject of the knowledge of God. Human beings can know God only by being given a knowledge which corresponds to God’s Self-knowledge. This occurs in that human beings are given the eyes of faith with which to discern that which lies hidden in the veil. Thus conceived, revelation is seen to have two moments; an objective moment (God veils himself in a creaturely medium) and a subjective moment (God gives us faith to know and understand what is hidden in the veil). The objective moment is christological; the subjective moment, pneumatological.
In the Göttingen lectures, the Kantian assumptions with which Barth works in explicating this point of view are especially clear. With Kant, Barth believes that human knowledge is limited to the intuitable, phenomenal realm. And this means that if God (who is unintuitable) is nevertheless to be intuited (and therefore known in the strict, theoretical sense) God must make himself to be phenomenal, that is, God must assume creaturely form. But at this point a further problem arises. In making himself phenomenal, God has entered into the subject-object relation in which the constructive role played by the Kantian categories of the understanding make the human knower the “master” in any and every knowledge relation. So the problem is this: How can God remain God (i.e. the Subject of the knowledge of God) even as God takes on phenomenal form? The answer has everything to do with the fact that God does not make himself directly identical with a phenomenal magnitude but only indirectly so. What occurs in revelation is that the divine Subject lays hold of or grasps the human knowing apparatus through the phenomena from the other side. In this way, the limitations placed on human knowing by the Kantian subject-object split are overcome by a transcendent, divine act.
It should be added that Barth secures the lordship (“mastery”) of God in this knowledge relation by insisting on its actualistic character. It is not the case that God unveils himself through the veil once and for all, as a completed act. If it were so, God would have ceased to act; nothing more would need to be done. But such a view cold be coherently explicated only by the thought that although God was once only indirectly identical with a medium of revelation, at some point in time God became directly identical with it. In this view, nothing further need occur from the divine side. The epistemic relation between God and the human knower would have become fixed, stabilized. Having begun in a relation of absolute epistemic dependency, the human knower would once again have attained the mastery in this relation. To all of this, Barth said no. God is indirectly identical with the medium of his Self-revelation not only before revelation occurs but during the revelation even and after it. Thus Barth could consistently overcome the limitations placed by Kant on the knowledge of God only by insisting upon the actualistic nature of the epistemic relation.
One final clarification: for those of us who are “disciples at second hand,” the place at which God finds access to us (and therefore we to God) is not longer Jesus of Nazareth (who has “ascended on high”); it is, rather, through the medium of the witness of Holy Scripture that God continues to unveil himself. For us, knowledge of God occurs when and where God takes up the language of the biblical witness and bears witness to himself in and through its witness (the objective moment) and awakens in us the faith needed to comprehend that witness (the subjective moment). In that this occurs, a relation of correspondence (the so-called analogia fidei) is established (actualistically!) between God’s knowledge of himself and human knowledge of God. This it is quite clear that the motor that drives Barth’s theological epistemology is the Realdialektik of the divine veiling and unveiling.
Much to digest. I think that what is covered by McCormack in regard to Barth is THE most important locus of theology. In other words, how we come to think about how we have knowledge of God has a prior notion informing it in regard to who we think God is; this seems to be a paradox, or a dialectic. Indeed. I think, often, people just take for granted a certain theological tradition with all of its trappings without considering what in fact those trappings are and where they come from. So we have formal and material realities mutually implicating each other insofar as the object of theology is related to its subject and vice versa. What I think is most important to recognize is that if we presume that we are talking and writing about God as theologians that we’d better have a sound basis for asserting that we are indeed thinking God from God. This is where the classical theistic approach fails in my view. It starts with a ground for knowledge of God in the being of humanity abstract from God, albeit preveniently informed by God’s grace (understood in qualitative terms); a ground that is not grounded previously in God’s being, only upon the asserted supposition that all being is sourced in God’s. Do you see the problem with this? It does not overcome what Barth overcomes in the Kantian form of such knowing; a form of knowing where the human ‘knower’ is the ‘master’ of the knowing apparatus that allows them to assert that they have a point of contact with God outwith a previous ground in God (in a theological taxis ‘order’). This is the genius of Barth’s proposal; it grounds knowledge of God in God and extends that by his grace (who is the Christ) out to us, brings us into that center of knowing by the Holy Spirit, and allows us to think God after God has already thought himself for us in Jesus Christ. So the Deus absconditus is the Deus revelatus.
Theologians will keep on theologizing in their received traditions of theologizing, but for my money I can’t really see how what they are ultimately articulating has much to do with a knowledge of God that is itself grounded in the Self-knowledge of God. I would suggest that the tradition has stumbled upon proper aspects of knowledge of God only insofar as it has sought that in its disclosure borne witness to in Holy Scripture. In other words, the tradition has offered certain categories toward a knowledge of God that have relative gravitas to them only as that has incidentally been arrived at by the theologian’s willingness to seek for such knowledge in Holy Scripture.
 Bruce L. McCormack, Orthodox and Modern: Studies in the Theology of Karl Barth(Grand Rapids, MI: Baker Academic, 2008), 109-12.