It has always been the prerogative of Christians to claim to have knowledge of God, but upon what basis? Throughout the development of Christian theology (over the many centuries) there has pretty much been a dominant way to do that; that way is typically by one way or the other appealing to a philosophical speculative process in constructing a conception of godness (e.g. by abstractly reflecting upon nature, whether that be creation in general or humanity’s ‘being’ in particular), and then taking these conceived categories to Christian ‘revelation’ found in Scripture, about God, and attempting to synthesize the God revealed therein (and the God revealed in Christ) with these philosophical categories. Most Christian theologies that you have ever been exposed to as a Western Christian (or even Eastern one) involves this kind of process; so this we could say has become the ‘orthodox’ standard or rule for thinking God, as both one and three (or triune). But is this the best way to conceive of God, is this the only way we should conceive of God? Is this the only way that does justice to the God disclosed throughout salvation history recorded in the so called Old Testament writings, as well as the God ultimately revealed in the New Testament in Jesus Christ? That seems to be the consensus among most evangelical (and Reformed, as well as Lutheran) thinkers and theologians. But why?
The New Testament, in the fourth Gospel says this:
The phrase translated ‘made him known’ comes from the Greek word ἐξηγήσατο; it is where we get our word ‘exegesis’ from. So according to the Gospel writer, Jesus alone has the ability to exegete who God is. Does this then mean that we shouldn’t look elsewhere to conceive of God, like philosophy, as the classical and ‘orthodox’ approach has done for centuries? Isn’t it possible to take philosophical categories and reify (make something abstract or foreign to a particular context, concrete in a new context) them in a way that those categories become affectively pressurized under their new conceptual context, such that the revelation itself is determinative of meaning? This procedure can be appealed to, I would contend, but only as an internal apparatus, not one that is constructed prior to being confronted with the reality of God’s Revelation. For example: the Trinity. The Trinity is a many splendid and mysterious Christian reality, and the Patristic church was confronted with the challenge of attempting to create a grammar to articulate it. So they moved from being confronted with this challenge Revelationally to utilizing some Greek metaphysics in order to do that. But you see the order here; the move was from revelation to the utilization of philosophy, and then the utilization of philosophy was “reified” in a way that it truly became a grammar determined to be what it was (conceptually) by the revelation and not vice versa. And so what we have here then is a kind of above to below movement in the task of knowing God and making him known. Kevin Diller comments in this way as he discusses Karl Barth’s relationship to this order of knowing vis-à-vis the philosopher’s way versus the theologian’s way:
… As fellow human beings engaged in this enterprise, the philosopher and theologian are companions. Barth says they face “common difficult tasks.” But it is exactly this commonality that gives rise to a turf-war-like confrontation. It is the way in which philosophy approaches the Truth that has provoked theology to take its artificially independent stand. The theological way of knowing is “motivated wholly by the power of the primordial movement from above to below. The theologian stands and falls with this sequence, in fact, with its irreversibility.” It is significant to note that Barth sees the movement from below to above as legitimate and important, but only as a secondary movement from the first movement that is irreversibly from above to below….
Even for Barth, in light of Diller’s comments there is some room for a proper deployment of philosophy; but in order for that to happen accurately it must happen from a right order (taxis) of ‘being’ to ‘knowing’. Revelation must always stay in the dominant role in dictating and imposing its reality and meaning upon our knowing and being. And Barth believed, as do I, that much of the classical approach (because of the impact of medievally received Aristotle through Thomas Aquinas and others) ended up losing its way, and allowing speculative philosophy and categories developed from that mode to distort how we think of God in Christ. Here is what Bruce McCormack writes in regard to Karl Barth’s approach principled as it was in a Christ centered way:
On the basis of this Self-revelation, he then asked, what must God be like if he can do what he has in fact done? What is the condition of the possibility in eternity for the incarnation, death, and resurrection of the Son of God in time? In taking this approach, Barth was taking a principled stance against the more traditional procedure (followed in large measure by Schweizer) of beginning with an “abstract” concept of God (which is to say, one that has been completely fleshed out without reference to God’s Self-revelation in Christ) and only then turning to that revelation to find in it confirmation of what was already attributed to God without it. Such a procedure, as we have already seen in relation to Schweizer, determines in advance what revelation in Christ will be allowed to say. Against this procedure employed by theism in all of its forms (classical and neo-Protestant), Barth proposed to work in an a posteriori fashion, beginning not with a general concept of God or a general concept of human being but with a most highly concrete reality, Jesus Christ. And so, if God has in fact done something, it will not do to say that God cannot do it. Theologically responsible reflection will only be able to ask, What is the eternal ground for God’s acts in time?
Is there room for an ‘orthodox’ way of doing theology, for thinking about God? I would say, if in fact that kind of orthodox way is given shape by appeal to speculative (via negative) categories for how God must be, then the answer must be No! And, I would suggest that all you need to do is do a little bit of digging into the neo-Protestant, post Reformed orthodox mode of doing and thinking theology (Francis Turretin is a good place to start), and you will quickly see how God has become captive to this kind of orthodox God talking and articulating.
As Christians, I would suggest, it only makes sense to limit our knowledge of God, categorically, to the Incarnation; even if this kicks against the so understood “classical” and “orthodox” way. We live in the 21st century, and Jesus the Teacher of the church still speaks, and he speaks through the various periods of the church. I am not advocating (nor is Barth) a complete abandonment of all the theology about God that developed in the medieval period (God forbid it!) I am advocating though that we repudiate a kind of metaphysicalism that appeals to something (other than revelation) before we get to God (philosophy), until we have met God in Christ; and when we repent of such theologizing and adopt a truly principled and Christ concentrated way, then I believe we can better interrogate and employ even some of the classical insights in regard to a doctrine of God.
 Kevin Diller, Theology’s Epistemological Dilemma: How Karl Barth and Alvin Plantiga Provide a Unified Response (Downers Grove, IL: Intervarsity Press, 2014), kindle loc. 937.
 Bruce L. McCormack, Orthodox And Modern: Studies in the Theology of Karl Barth (Grand Rapids, MI: Baker Academic, 2008), 58.