The Deus absconditus (‘hidden God’) is the Deus revelatus (‘revealed God’) in Jesus Christ. But how do we know this? Because Jesus said so; He demonstrated so. A genuine Christian theologian isn’t given to fits of speculation about godness. A genuine Christian theologian is definitionally such simply by the confession that they are Christian. But much 
of this has gone by the wayside in the development of dogma in the catholic Church. In Latin theology for example, where Thomas Aquinas has been canonized, for both the Catholic and Protestant theologian alike, the method for developing a doctrine of God is based in speculation, and an analogia entis (‘analogy of being’). But this kicks against the premise of Scripture itself. Holy Scripture is Holy without proof. In other words, God just shows up in Scripture. He says I AM. Likewise, Jesus says: I AM. This represents the character or ethos of a genuine Christian theology. That is, the Christian knower of God only knows who (and even what) God is by way of God’s Self-revelation in Jesus Christ. It is as the Christian comes into union with Christ by the Spirit that they come to have a genuine ground for thinking who God is; that is, a ground grounded in Godself for us in Jesus Christ. In other words, in this frame of relation, the Christian can think and know God concretely as they have been granted eyes to see and ears to hear from Christ’s vicarious eyes and ears for us in His mediating humanity. It is here that the Christian theologian can know, think, and speak God. It is in this Holy and sanctified ground where the Christian’s knowledge of God isn’t based in a center in themselves (and thus a speculative, discursive model), but from the center of God for us in Jesus Christ.
The aforementioned is what characterizes Karl Barth’s way for thinking and doing Christian theology. For Barth, and for me, the centraldogma of Christian theology is Jesus Christ. We know this because in the Dominical teaching Jesus says that the ministry of the Holy Spirit, who inhabits the Christian’s heart now as a guarantee, is radically Christ concentrated. The Holy Spirit isn’t given to fits and flights of speculation of an abstract notion of godness; nein, the Holy Spirit’s sole ministry is to push us deeper and deeper into the words and reality of Jesus Christ. It is from whence that the Holy Spirit comes alongside, hovers about, and comforts us. Not by pointing us to an actus purus (‘pure being’) notion of God, but pointing us to the Son of the Father (see Jn 14—16).
With the above in mind lets read along with Bruce McCormack as he describes Barth’s approach to knowledge of God, which is both a terminological analogia relationis (‘analogy of relation’) and analogia fidei (‘analogy of faith’).
. . . Beintker says, ‘the Denkform of the analogia relationis sive proportionalitatis, which sets forth a correspondence between the God-human relation and the human-human relation, forms a constant in Barth’s work from the time the Tambach lecture on.’[1]
The crucial passage appealed to in order to confirm this view is this: ‘The human being does indeed do something corresponding, parallel, analogical in her own creaturely sphere of being in view of that which God does in His, in that He reveals Himself.’.. . What is at stake in this passage is indeed an analogical relation between divine speaking in the act of revelation and human knowing in the act of faith. Beintker is right to see in this an example of what Barth would later call the analogia fidei. It must be pointed out that the Göttingen Prolegomena only came into Beintker’s possession as he was correcting the final draft of his book for publication. Had he had the earlier version of the prolegomena, he would have had to adjust his thesis slightly, placing the first instance of the analogia fidei in 1924 rather than 1927—as he himself implicitly acknowledges through the provision (in the final draft) of the parallel passage in Unterricht to the one just quoted.[2]
McCormack continues:
The ‘analogy of faith’ refers most fundamentally to a relation of correspondence between an act of God and an act of a human subject; the act of divine Self-revelation and the human act of faith in which that revelation is acknowledged. More specifically, the analogy which is established ins a revelation event is an analogy between God’s knowledge of Himself and human knowledge of Him in and through human concepts and words. There are three aspects of this analogy which need to be highlighted. First, the analogy in question is not posited with creation. It is not an analogy between the being of Creator and the being of the creature—which Barth refers to as an analogia entis in contrast to an analogia fidei. The focus here is not being but rather a highly concrete event: the event of revelation. Second, there is nothing in the being or knowing of the human subject which helps to bring this event about—no capacity or pre-understanding which might be seen as a necessary precondition to its occurrence. The only capacity needed for the analogy is one which God Himself graciously provides in the event itself as a gift, namely faith. In the event of revelation, human knowledge is made by grace to conform to its divine object. Thus (the reader will forgive an overused metaphor, but it is good Barthian language), the direction in which the analogy works is always ‘above to below’. That is to say, God’s Self-knowledge does not become analogically related to a prior human knowledge of Him in revelation; rather, human knowledge is conformed to His. God’s act is the analogue, ours is the analogate; His the archetype, ours the ectype. Third, the ‘analogy of faith’ is to be understood ‘actualistically’, that is, strictly as an event. The relation of correspondence which is established in the revelation-event endures. Thus, the ‘analogy of faith’, once realized, does not pass over into human control. It must continue to be effected moment by moment by the sovereign action of the divine freedom if it is to be effected at all.
The central area of theological reflection to which this understanding of analogy was applied by Barth is that of the relation of the content of revelation to human language (concepts and words). Barth’s view is that human language in itself has not capacity for bearing adequate witness to God. If human language is nevertheless able to bear witness, it will only be because a capacity not intrinsic to it has been brought to if from without. But that is grace, not nature. In a gracious and sovereign act, God takes up language of human witnesses and makes it to conform to Himself. God must therefore speak when spoken of by human witnesses if such witness is to reach its goal. He must reveal Himself in and through the ‘veil’ of human language. It is at this point that the inherently dialectical character of the analogia fidei is seen.[3]
There are many trails we could take out of this concise explication on Barth’s analogia relationis-fidei, but let me highlight just a couple. The basic premise of Barth’s et al. understanding of the analogia fidei versus an analogia entis is anthropological; but of course, as is typical with Barth, anything that is anything in theology is first and always Christological. What is underwriting Barth’s doggish commitment to his ‘analogy of faith’ is the biblical teaching of a radical human depravity. You will notice that as McCormack was sketching these things for us, he kept pressing that in Barth’s theology God acts both sovereignly and unilaterally for us; if He didn’t, then knowledge of God left to our own machinations could only conclude in idolatry. So, for Barth (for me) there is no ‘grace perfecting nature’ or ‘revelation perfecting reason,’ there is only the impossible possibility that has actualized in the event of God’s free choice to Self-reveal for us in Christ. In Barth, as we also observed in McCormack’s development, there is nothing inherent to natural humanity (because of the fall) that could correspond, even analogously, to a knowledge of who and what God is; again, such endeavor could only end in an idolatry of self-projection. This is key, when considering Barth’s thinking on his ‘analogy of faith’: i.e., human language in itself, or by nature (precisely because of the fall) has been lobotomized to the point that it can only operate in sub-human ways. As such, when a ‘natural’ person, such as the classical philosophers, attempt to think God, all they can do is build a construct based on negation; all they can do is look within, negate their obvious finity, and then posit that God must be humanity’s opposite and thus infinite so on and so forth.
Hopefully, if you were wondering about these things, this post has cleared it up for you.
[1] Bruce L. McCormack, Karl Barth’s Critically Realistic Dialectical Theology: Its Genesis and Development 1909—1936 (Oxford: Oxford University Press, 1997), 10 n. 32.
[2] Ibid., 10-11 n. 33.
[3] Ibid., 16-18.