The ‘being’ (ousia) of God is largely, is hugely important when it comes to differentiating what we are doing in Evangelical Calvinism versus classical (Federal) Calvinism. If you peruse my blog you might find that addressing this point is something of a theme by now. In order to keep in theme I thought I would post another post that engages with what I would claim, despite those who protest this, that Post Reformed orthodox theology operates from a Pure Being theology and doctrine of God. In other words, even though folks like Richard Muller argue otherwise, it is very hard to see how this just is not the case. What Pure Being theology (like that produced by appropriating classical philosophy with Christian theology i.e. Aristotle et al.) gives us is a God who must engage with his creation through impersonal decrees; he must somehow keep himself untouched by his creation. We end up with an impersonal God who engages with us through laws and decrees, and not with the personal touch we might expect a God who is Triune love to engage his creation with. Here is how Richard Muller argues this:
Etienne Gilson makes the very pointed remark, in The Spirit of Medieval Philosophy, that the great source and starting-point of all medieval discussion of the being and essence of God is not Greek philosophy in general or Aristotle in particular, but Moses—in Exodus 3:14: “God said to Moses, ‘I am who I am.’” Nor ought we to attribute the use of Exodus 3:14 as a reference to the being of God as a result of ignorance of Hebrew and dependence on the sum qui sum of the Latin Vulgate. We read, for example, in the Guide for the Perplexed of Moses Maimonides,
God taught Moses how to teach them and how to establish amongst them the belief in the existence of Himself, namely, by saying Ehyeh asher Ehyeh, a name derived from the verb hayah in the sense of “existing,” for the verb hayahdenotes “to be,” and in Hebrew no difference is made between verbs “to be” and “to exist.” The principle point in this phrase is that the same word which denotes “existence” is repeated as an attribute…. This is, therefore, the expression of the idea that God exists, but not in the ordinary sense of the term; or, in other words, He is “existing being which is the existing Being,” that is to say, the Being whose existence is absolute.
Of the Holy Name, Maimonides adds, “the tetragrammaton … is not an appellative; it does not imply anything except his existence. Absolute existence includes the idea of eternity, i.e., the necessity of existence.” The point must be made, with respect to Gilson’s remarks, that however much the classical philosophical heritage influenced scholastic formulation, the form that the influence took and, indeed, the medieval interpretation of the classical sources, was in large measure determined by biblical exegesis—and that, granting the Greek philosophical sources of medieval Jewish and Christian conceptions of God, those sources, taken by themselves, do not by themselves account for either the theology or the metaphysics of the medieval thinkers.
We must take exception to often-uttered claims that descriptions of God in terms of “substance” and “essence” lead ineluctably “to the unfruitful abstractions of the conception of God in Greek philosophy,” or that language such as that of Aquinas concerning God as “supremely existent” (maximè ens) is a “Grecian” as opposed, presumably, to a “religious conception of God.” Such claims assume, first, that discussion of the divine essence is a fundamentally Greek enterprise (if Gilson and Maimonides are correct, it is not) — and second, quite arbitrarily, that abstraction is both characteristically Greek and quite “unfruitful” and, in addition, is somehow divorced from the “religious conception of God.” We ought not to accept any of these comments uncritically, nor ought we to suppose that the medieval development of concepts of God as willing, as thinking, as loving, and as, by nature, spirit (none of which are without “religious” implication), can be severed in a facile manner from the issue of the divine being or essence.
Okay, so we see Muller among many of his contemporaries claiming that the classic Reformed were just doing good biblical exegesis and not borrowing their conceptual apparatus from the Greek philosophers. But when you actually read Reformed theology, particularly in the 16th and 17 centuries, and even now as that gets repristinated in the 21st century, it makes you wonder how Muller et al. can claim what they do.
As an alternative T.F. Torrance highlights the role that the Hebraic mind and categories played in early ecumenical thinking when it came to conceiving of God by way of his Self-naming to his covenant people. This is ironic, really, because Torrance is addressing the same tetragrammaton context that Muller is; yet they arrive at totally different conclusions. Here is what Torrance has to say in this regard:
I have been directing considerable attention Hebraic way of understanding I am or ἐγώ εἰμί of God to which the Early Church so often appealed in seeking to understand the Being or οὐσία of God, for it is very different from the static metaphysical notion of essence or substance found in the Greek philosophical tradition. The Being of God, known only in the fellowship created through his personal self-naming, self-affirming and self-giving to his people, is the living dynamic Being (zwsa kai energhtikh οὐσία) of God’s redeeming presence to them, with them and for them. It is to be understood not simply in terms of the self-grounded Being of God, but as the Being of God for others with whom he seeks and creates fellowship, although that is to be regarded as flowing freely from the ground and will of his own transcendent Self-Being. While the Being of God is not to be understood as constituted by his relation to others, the free outward flowing of his Being in gratuitous love toward and for others reveals to us something of the inmost nature of God’s Being, as at once transcendent and immanent — God in the highest and God with us and for us, the divine ousia being understood as parousia and the divine parousia being understood as ousia. Hence it may be said that the Being of God is to be understood as essentially personal, dynamic and relational Being. The real meaning of the Being or I am of God becomes clear in the two-way fellowship he freely establishes with his people as their Lord and Saviour, for it has to do with the saving will or self-determination of God in his love and grace to be with them as their God as well as his determination of them to be with him as his redeemed children.
There is a deep personalism informing the type of Trinitarian conception of God’s Being that Torrance describes and develops for us. Not of the existentialist type that so many classical theologians worry about today, particularly when it comes to modern theology in general, or maybe even Barth and Torrance in particular. The personalism that Torrance pushes us into is informed by what we find the ecumenical Patristic theologians working with; one that is oriented from the type of Hebraic mode of thought that Torrance alerts us to. A personalism that is truly relational insofar as that relationship is defined by God in his inner and eternal life as Father, Son, and Holy Spirit which we are then included within by way of God’s gracious and free choice to be for us and with us which allows us to be eternally within him in the Son, Jesus Christ.
While much of this might sound academic, it really isn’t. It has profoundly pastoral and practical implications for someone’s daily spirituality. Who we think God is determines everything else downstream, even how we live before and with God. Who God is will impact what it means to be creatures in the image of God; it will determine the way we understand grace and what it means to have grace in the conversation of our Christian lives; both in the church and outside of it. These are not merely academic platitudes; they are real life and significant issues for every single Christian and non-Christian alike. How we understand God, and who we understand him to be, and from whence find basis for that will determine everything else.
 Richard A. Muller, Post-Reformation Reformed Dogmatics: The Divine Essence and Attributes, Volume Three. The Rise and Development of Reformed Orthodoxy, ca. 1520 to ca. 1725 (Grand Rapids, Michigan: Baker Academic, 2003), 50-1.
 Thomas F. Torrance, The Christian Doctrine of God: One Being Three Persons (London: Bloomsbury T&T Clark, 2016), 123-24.