There is a lot of talk about ‘substance theology’ these days, and in the past days. Indeed, substance language marks classical theism as the way to talk God at least since the days of Thomas [of Aquino], if not further back since the Greeks started using the language of ousia or ‘being’ for talking God (but that was a little different from the Thomist heritage in 
the sense that they often used ousia as synonymous with hypostases or ‘persons’ and vice versa). No matter what period past to think and talk God in terms of substance has become considered the orthodox way, the way of the consensus fidelium, the way of retrieving all that is holy and orthodox in regard to talking and thinking God. Any verging from substance metaphysics, especially as we have developed into Enlightenment and Post-Enlightenment ways, is considered heresy by the faithful. Indeed, if you scan various literature, and even online conjecture, what you will often find in such quadrants is that anyone who attempts to think God in overt ‘personalist’ or personal terms must be some sort of heterodox, at best, and heretic at worst. The label the faithful place on those who would attempt to think and talk God in overtly personalistic terms is: ‘theistic personalism.’ Such people want to claim that said theistic personalists, in regard to talking and thinking God, are nothing better than ‘social Trinitarians,’ thus operating from a panentheist view of God wherein God is thought purely from below to above. This is the charge made against those of us who would fit the so-called theistic personalist label, and yet it fails to recognize the argument of the beard it thinks from; it fails to make distinctions on a continuum; it fails to recognize that God Self-revealed is Father of the Son / Son of the Father by the Holy Spirit—these are ultimately personalizing personal terms and realities ‘revealed’ about who God is. Thusly, it is important to allow such revelation about God to determine the way we think and talk God. And if ‘substance’ language were to be used it would have to be reified by the pressures provided for by the Self-revelation of God, otherwise the “substance-abusers” (haha) would be the ones guilty of a social Trinitarianism; i.e. of importing concepts from below to the above, in regard to God (in fact this is exactly what obtains, I would argue, when such substance-abusers attempt to think God from His effects in the created order; to think God from the so-called analogia entis).
With the aforementioned noted I think it would be interesting to observe how things transitioned from thinking and talking God in terms of substance to subject (or in personalist terms). Eberhard Juengal offers a helpful sketch of how this transition took place in the ‘theology’ of Hegel (which of course post-Hegel would have far-reaching implications towards the development of a so-called ‘modern theology’). Juengal writes:
These distinctions between the three forms of religion are only apparently formal. They have their effect in the content of the religions. This can be shown in the statement about the death of God, which belongs to revealed religion, statement which formulates a precise step of the relationship of being and consciousness, a relationship which is so decisive and full of tension for the history of the spirit. That being which is independent of any other, “. . . that which is in itself, and is conceived through itself,” has been called “substance” ever since Aristotle. It is characteristic of substance that it does not exist in something else. According to Hegel, this distinguishes it from the subject. Whereas substance rests in itself, for Hegel the subject is “the process of positing itself, or in mediating with its own self its transitions from one state or position to the opposite. The subject comes to itself whereas substance has always been in itself. The essence of substance is autonomy, that of the subject is self-movement. Part of the self-movement of the subject is mediation by something else, which for its part is what it is through the subject. And the subject does not lose itself in that other thing, but rather together with that other thing, which exists because of it, it arrives at a freedom which surpasses the autonomy of substance, the freedom of self-consciousness. Therefore, in Hegel’s view, “. . . everything depends on grasping and expressing the ultimate truth not as Substance but as Subject as well.” Only a substance which has become absolute subject and which is understood as absolute subject can be regarded as God. From this point of view, the differentiation of the three forms of religion has taken place. They mark the pathway of the substance toward its being a subject.[1]
If you have ever heard the language Being in Becoming with reference to God, what Juengal describes above, with reference to Hegel, would be where such language and conceptuality comes from. It is this ‘turn’ to ‘Being in Becoming’ that many classical theists maintain results in collapsing God into the modalism of the economic, or the ‘world-being’ (my word), such that God becomes a predicate of His becoming. But even as noted in the sketch of Juengal, this would be wrong-think. For Hegel, according to Juengal, there would be no becoming without the prius of God’s life as “substance,” or antecedent-being. Of course, the type of dialectical inflections this takes in the Hegelian system is a thing of its own imagination, but his development, even as he has described this type of distinction between substance and subject, is not the only or necessary way to think and talk God as ‘Being in Becoming.’
A good reading of Barth’s theology, as Juengal offers in his book God’s Being Is in Becoming: The Trinitarian Being of God in the Theology of Karl Barth, identifies a way to think in potentially “Hegelian” terms without actually becoming (pun intended) Hegelian; just as Barth thinks in Kantian terms without actually becoming Kantian. It is possible to reify grammar, just as the Nicenes did with the Hellenic language (of substance or ousia) at their time, and end up with a linguistic and conceptual sitz im leben wherein the [Hellenic, or Hegelian et al.] ‘text’ simply becomes a pre-text awaiting the re-texting provided for it by an alien reality—in the case of Christian witness, the Kerygma—such that a non-correlationist Christian grammar is produced without the metaphysical baggage that originally gave rise to said grammars in their original (Hellenic, Hegelian, Kantian et al.) contexts. The question always remains: is there a better context-laden grammar out there, that is for thinking and talking God, than other alternatives might offer? This is the question that ought to drive all constructive and Church dogmatic theological endeavor, but it doesn’t. So, instead we end up with the substance-abusers calling the constructivists (which is what Thomas was during his day, by the way) that nastygram: “theistic personalists.”
The point in all of this, for me, and hopefully for you, is to recognize that theology has developments; some good, some bad. But what should be indicated here is that good theology is always already developing, and that it isn’t slavishly domiciled into one supposed ‘sacrosanct period’ of an ostensibly orthodox development of being. God still speaks, in other words: Deus dixit.
[1] Eberhard Jüngel, God as the Mystery of the World (Eugune, OR: Wipf and Stock Reprint Mohr Sieback, 1983), 80-1.