What does theology study and how does theology study what it studies? This inquiry of figuring out what theology is and what it studies and the manner in which it studies pertains to theological prolegomena. Theological prolegomena prepare the mind for theological inquiry. It must be noted, however, proceeding with prolegomena is not slapping an introduction to theology in such a way that theology’s object does not govern the prolegomena. Surely theology has no need to be introduced. Instead, “determining the possibility, nature and responsibilities of theology requires appeal to material theological doctrine. Indeed, prolegomena to systematic theology are an extension and application of the content of Christian dogmatics . . . not a ‘pre-dogmatic’ inquiry into its possibility.” And so, theology’s content will shape what we have to say about its prolegomena. In this prolegomenon of systematic theology, we will cover theology’s object, arrangement, and the distribution of the doctrine of God and creation. Specifically this essay is a prolegomenon that explicates what theology studies, how theology studies it, and why theology studies what it does in a peculiar manner.
Christian doctrine can be structured with two parts: “God himself and the outer works of God,” but yet, “in one sense, there is only one Christian doctrine, the doctrine of the triune God, because in following that doctrine to its end theology will treat all the topics customarily brought together in a systematic theology.” However, this is prone to receive rather unhappy charges. Another way of putting it is thus: theology has one two-fold object, that is, there are two distinct, yet inseparable topics in theological inquiry: God and everything else by way of relation to God. We might describe the first topic as God’s life, both ad intra et ad extra, and the second is all things that are not God—creation.
God the Trinity
Theology’s principle object is God himself. Nevertheless, because God is and acts, we must cover God in two aspects: absolutely (ad intra) and relatively (ad extra). First and foremost, Christian dogmatics covers God’s wholly realized life as Trinity in its absolute fullness, self-existence, simplicity, and self-standing perfection “apart from any relation to creatures.” In short, theology looks to God’s inner life—the ontological or immanent Trinity. In considering this infinite object, similar to Thomas Aquinas’s structure of his Summa Theologiae, theology studies the divine essence and attributes, and (then) the divine persons in their intratrinitarian relations or origin (i.e., the divine processions) and their personal properties as Father, Son, and Spirit. This is not to split or sever the concepts of Deus unus or Deus trinus, but it is a (well-tested) sequence that appears to follow divine revelation and prepares the mind to understand the divine persons, for “one cannot conceive of the person without the substance or without the nature belonging to the very ratio of the divine persons.” And due to divine simplicity, when we cover the divine persons, we are crucially still talking about the divine essence.
All our studies—whether it is Paul’s ethics, Greek syntax, atonement in the Patristics, or tracing the biblical-theological themes of temple or sonship—are directed to their beginning and end, namely, God in himself. And so, theology’s primary object is none other than θεός (theos; the etymological connection is not to be missed) considered in his opera Dei ad intra (inner works), which are his life of plenitude and perfection in the divine processions and are the ground of his transitive works in the economy. If we tend to speak on phenomena and creaturely being, thinking that it is much more manageable, relatable, and valuable, and so our theology does not end in consideration of God as he is, our theology is no longer theological.
Second, theology in turn considers God relatively, that is, in his outer works (opera Dei ad extra) or stated as the divine missions. This aspect focuses on God’s works that finds it termination in creation. Since God’s inner life precedes and grounds his external works towards creatures, this aspect “is a derivative element of theology’s attention to its principle matter.” That is, God’s external works flow forth from himself and thus (1) are constituted by God’s inner life, (2) are thus point back to God’s inner life, and (3) are an extension of God’s life in which the missions contain the processions. Therefore, the opera Dei ad extra must be referred to the opera Dei ad intra, which are their ground. Nonetheless, because God has acted thus, we are required to talk about God’s external works, but we are to do so as they are “intelligible only as they are derivative,” and therefore distinct as an extension, “from the eternal divine processions.”
After considering God, theology then covers everything else—all that is not God. If we disregard this topic as irrelevant and without value, seeking only to talk about God, theology fails to be theological. However, this is not because creation adds anything to God or that creation has any claim to be considered as most prominent or “intrinsic” to “theological attention.” But rather, once again, because God has so acted to bring about life. Hence, we study that which is not God because God is and God acts, bringing something else into being. We could state it this way: theology that fails to speak of created things fails to speak of God, not because they are God, but because from God’s perfect life flows forth his external works whereby he gives life to creatures. Nevertheless, created things are treated secondary because they were once not, and are that which might not have been. With this in mind, we can now turn to the arrangement and manner in which we treat these topics.
Theology’s manner, arrangement, and order follows the actual sequence of how things are. Further, it not only follows how things are, but it follows biblical order from God to economy to redemptive history. If we study things for what they are (i.e., God as God, and creatures as creatures), theology’s arrangement ought to follow the material order of its object, and so, follow the ordo essendi (the order of being). Put differently, the object of theology should shape and determine not only what we study, but how we study it. If the material sequence is divine essence –> God’s works ad extra –> creatures, then our arrangement and order should be likewise, especially in treating and part of the doctrine of creation. With this in mind, then, theological method matches its material, and so, we study things not only for what they are, but in what manner they are.
“Arrangement is determined by [theology’s] matter, and, once again, the matter of theology is God either in himself or relative to creatures.” Theology, therefore, begins its inquiry first with God’s inner life as Trinity, and then moves outwards to consider his works and his creation. And so, when we study both God and his economy, we study them in a particular manner and not as a loosely gathered “string of topics” without any coherence. Again, first, we talk about God apart from his creation, that is, God in se, and then, second, we talk about creatures only in their relation to God, since they exist from and wholly dependent upon him as their source, Creator, Provider, and end. Thus, when we turn our inquiry to created things, we do not stop talking about God. In talking about all things that are not God, then, “theology talks about everything by talking about God.”
Since God is the principle object of theology, theology ultimately talks about God, and “talk about God not only describes the matter into which theology enquires but also, crucially, informs its portrayal of its own process on enquiry.” Despite charges it may receive, John Webster says that a good principle of arranging doctrines goes as follows: “in an important sense there is only one Christian doctrine, the doctrine of the Holy Trinity in its inward and outward movements. Whatever other topics are treated derive from the doctrine of God as principium and finis.” Such arrangement and method is not novel or exclusive to Webster, but has roots in those of the past in Medieval and Protestant traditions. For example, in a rather lucid passage, Bavinck writes:
When it turns its attention to creatures, it views them only in relation to God as they exist from him and through him and to him [Rom. 11:36]. So the, the knowledge of God is the only dogma, the exclusive content, of the entire field of dogmatics. All the doctrines in dogmatics––whether they concern the universe, humanity, Christ, and so forth––are but the explication of the one central dogma of the knowledge of God. All things are considered in light of God, subsumed under him, traced back to him as the starting point. Dogmatics is always called upon to ponder and describe God and God alone, whose glory is in creation and re-creation, in nature and grace, in the world and in the church. It is the knowledge of him alone that dogmatics must put on display.
Likewise, Aquinas says, “sacred doctrine does not treat of God and creatures equally, but of God primarily, and of creatures only so far as they are referable to God as their beginning or end”; and, “in sacred science, all things are treated of under the aspect of God: either because they are God Himself or because they refer to God as their beginning and end.” With this in mind, we might describe systematic theology as a peculiar and coherent science oriented to and shaped by its single, two-fold object of inquiry, which is God and all things as they relate to God.
From all that was above, it is quite clear that some doctrines that hold special and unique places in the Christian corpus.
The Holy Trinity
The doctrine of the Trinity has magisterial and governing rule over all other doctrines. No doctrine other than the Trinity may claim to be the articulus stantis et cadentis ecclesiae (the article of which the church stands and falls). The doctrine of the Trinity rules over, shapes, and determines all other doctrines. Hence, “the doctrine of the Trinity is not one doctrine among others; it is foundational and pervasive. To expound any doctrine is to expound with varying degrees of directness the doctrine of the Trinity; to expound the doctrine of the Trinity in its full scope is to expound the entirety of Christian dogmatics.” This stunning statement is clearly not just one about form and arrangement, but also material. The doctrine of the Trinity is primary.
Creatio ex Nihilo (Creation out of Nothing)
However, there is another distributive doctrine in Christian theology: creatio ex nihilo—a cardinal doctrine indeed. Coming after the Trinity, the doctrine of creation also claims governing rule over everything that is not God. It governs how we understand, for example, anthropology, geology, mathematics, sin, soteriology, and eschatology. However, since “its scope is restricted to the opera Dei ad extra, its distribution is less comprehensive than that of the doctrine of the Trinity,” but nevertheless, “provides orientation and a measure of governance to all that theology has to say about all things in relation to God.” Hence, the doctrine of creation is similar to a vicegerent.
What necessarily follows from these formal claims is a material one: God and creation are essentially different. Therefore, they are to be treated as such, and the methodology of the ordo essendi along with the distinction between the divine processions and missions honors this reality. Building from this and grounding God’s works ad extra in his works ad intra, doctrines like creation, man, and salvation “are illuminated from within the doctrine of God.”
 Webster, “Principles of Systematic Theology,” in IJST, 56–57; cf. H. Hoeksma, Reformed Dogmatics vol. 1 (Granville: The Reformed Free Publishing Association, 2004), 24.
 Webster, “Principles of Systematic Theology,” 56–57; cf. O. Weber, Foundations of Dogmatics, vol. 1 (Grand Rapids: Eerdmans, 1981), 5.
 Webster, “Rector et iudex super omnia genera doctrinarium?” in God Without Measure, I:160; cf. Webster, “Principles of Systematic Theology,” 68.
 Webster, “What Makes Theology Theological?” in God Without Measure, I:213.
 Aquinas, Summa Theologiae Ia.1.3 ad. 1; cf. Ia.7.1 sed contra.
 Webster, “What Makes Theology Theological?” I:213.
 It seems Thomas knew this well. After building the divine attributes (qq. 4–10) upon simplicity (q. 3), he brackets them with the attribute of unity (q. 11). Closing the initial treatment of the divine essence, he appeals to the Shema for God’s unity (Ia.11.3 sed contra). And from this (OT) proof, he can then build upon it with trinitarian claims in the NT (Aquinas, ST Ia.27–43). See also Tyler Wittman’s rather stunning article, “‘Not a God of Confusion, but of Peace’: Aquinas and the Meaning of Divine Simplicity,” in MT 32:2 (2016): 151–169.
 Gilles Emery, “Essentialism or Personalism in the Treatise on God in Saint Thomas Aquinas?” in The Thomist 64 (2000): 535. Emery will go on to say: “In treating of the divine essence, Thomas thus treats of what is fundamentally required in order to account for the person and for the esse of the relation in God, and therefore in order to elaborate what is the pinnacle of the divine persons: the subsisting relations” (ibid., 535–536).
 Aquinas, ST Ia.1.7 sed contra.
 Webster, “‘It was the will of the Lord to bruise him,’: Soteriology and the Doctrine of God,” in God Without Measure, I:146.
 Webster, “What Makes Theology Theological?” I:214.
 Ibid., I:214.
 Ibid., I:214.
 Ibid., I:214.
 Webster, “Rector et iudex super omnia genera doctrinarium?” I:161.
 Preferably, I would rather move from talking about the content of theology to theology’s context, that is, its domain—the economy of salvation. However, space restricts treatment here. For a very bright and compelling treatment, see John Webster, “Biblical Reasoning,” in ATR 90 no. 4 (2008): 733–751 (esp. 735–738); also see Webster’s essay on “The Dignity of Creatures,” II:29–47. From this it would be fitting also to speak of theology’s objective external principium, Holy Scripture, highlighting its properties, truthfulness, and how it is God’s accommodation to bring heavenly things to earthly creatures.
 Michael Allen, “Knowledge of God,” in Christian Dogmatics: Reformed Theology for the Church Catholic, eds. Michael Allen and Scott R. Swain (Grand Rapids: Baker Academic, 2016), 26.
 Webster, “Trinity and Creation,” in God Without Measure, I:85.
 Webster, “Principles of Systematic Theology,” 67.
 Ibid., 68.
 Webster, “What Makes Theology Theological?” I:214–215; cf. Aquinas, ST Ia.1.7.
 Webster, “Non ex aequo: God’s Relation to Creatures,” in God Without Measure, I:117.
 See Aquinas, ST Ia.1.7 sed contra.
 John Webster, “Theological Theology,” in Confessing God: Essays in Christian Dogmatics II (London: T&T Clark, 2016), 25.
 Webster, “Rector et iudex super omnia genera doctrinarium?” I:161.
 Webster, “Principles of Systematic Theology,” 68. This should be radically clear: this does not mean there are not other doctrines, rather, it means that these doctrines are explained by talking about God (cf. Webster, “Non ex aequo,” I:117; Webster, “Rector et iudex super omnia genera doctrinarium?” I:161; Webster, “What Makes Theology Theological?” I:214).
 R. Michael Allen, Justification and the Gospel: Understanding the Contexts and Controversies (Grand Rapids: Baker Academic, 2013), 78.
 Bavinck, Reformed Dogmatics, II:29. Bavinck also says, “The Christian mind remains unsatisfied until all of existence is referred back to the triune God, and until the confession of the God’s Trinity functions at the center of our thought and life” (ibid., II:330). Additionally, he elsewhere says that when theology study creatures, it “starts with God and traces all things back to him” (ibid., II:474).
 Aquinas, ST Ia.1.3 ad. 1.
 ST Ia.1.7. Aquinas also says, “Of all these things, in truth, we treat in this science, but so far as they have reference to God” (ST Ia.1.7). Once more, “whatever other conclusions are reached in this sacred science are comprehended under God, not as parts or species or accidents but as in some way related to Him” (ST Ia.1.7 ad. 1).
 Or “distinct” (Webster, “Theological Theology,” 25).
 John Webster, “Creation out of Nothing,” in Christian Dogmatics: Reformed Theology for the Church Catholic eds. Michael Allen and Scott R. Swain (Grand Rapids: Baker Academic, 2016), 127; John Webster, “Introduction: Systematic Theology,” in The Oxford Handbook of Systematic Theology ed. John Webster et al. (New York: Oxford University Press, 2007), 2; I am indebted to Brady Bowman’s insights on this in an unpublished essay, “System and Theology” (Minneapolis, MN: Bethlehem College & Seminary senior thesis).
 Webster, “Principles of Systematic Theology,” 68. And so, claims that justification is such seems to be inadequate (Webster, “Rector et iudex super omnia genera doctrinarium?” I:168–170; cf. Allen, Justification and the Gospel, 3–26).
 Webster, “Rector et iudex super omnia genera doctrinarium?” I:159; cf, Webster, “Principles of Systematic Theology,” 68.
 Webster, “Non ex aequo,” I:117; cf. Webster, “‘Love is also a lover of life’: Creatio ex Nihilo and Creaturely Goodness,” in God Without Measure, I:99.
 Webster, “Non ex aequo,” I:117.
 Webster, “Trinity and Creation,” I:86.
 Gilles Emery, The Trinitarian Theology of St Thomas Aquinas trans. Francesca Aran Murphy (New York: Oxford University Press, 2007), 42–43; Webster, “Trinity and Creation,” I:85–86.