Having written about the Reformed orthodox endorsement of metaphysics (though not a simply agreed upon endorsement, it must be said; there was debate about the role and limits of philosophy in theology among the Reformed), it is also important, in order to fill out the historical picture a bit further, to note a common line of argument among the Reformed orthodox regarding the source and limits of natural theology.
While on the one hand, many Reformed were concerned to go beyond the reduction of metaphysics by such groups as the rationalist Socinians, they were on the other hand concerned also to limit what they regarded as an excess of metaphysics by many Roman Catholic groups. The result of this excess, they argued, was that principles of metaphysics came to be considered as principles of theology, and reason was promoted to the role of a judge of the faith.
In response to this the Reformed insisted that Scripture alone is the principle of our theology, and they insisted on the finitude and corruption of human reason. That is, as they put it, Scripture is the principium congnoscendi, it is the source and norm of our theological knowledge. According to the Reformed, the source and norm of metaphysics, the light of nature, is not the same as the source and norm of Christian theology.
Further, because human reason is finite, it is not competent to stand as judge over those mysteries that are above and beyond it. And further, because human reason post-Adam is fallen, it is further incapacitated. Reason, even in its pre-fallen or restored state, is always and only the means by, or instrument of, our coming to theological knowledge. It is never the principle or judge of that theological knowledge.
But that raises the somewhat vexed question, variously asked in church history: what about the theological truths that fallen, pagan authors seemed to have attained? Plato’s transcendent Good; Aristotle’s unmoved mover? Plotinus’ perfected One? And many others besides.
As in the broader history of the Christian tradition, so among the Reformed orthodox there were differences in the way they answered the question. One popular attempt to answer that question, at least among the British Reformed orthodox, was expounded in great detail by Theolophilus Gales in his four volume The Court of the Gentiles (Part I, Part II, Part III, Part IV).
The Court of the Gentiles was written, as Gale puts it, “to confirm the authority, and demonstrate the perfection of, the sacred scriptures” (Part 1:Advertissements). In order to confirm the perfection of the sacred scriptures, Gale takes up a line of argumentation that had an ancient pedigree in the Christian tradition: “the wisest of the heathens stole their choicest notions and contemplations, both philologic, and philosophic, as well as natural and moral, as divine, from the sacred oracles” (Part 1:Advertissements; as for its ancient pedigree, Gale cites Josephus, Origen, Clement of Alexandria, Eusebius,Tertullian, Augustine, andJohannes Grammateous). That is, the truths that can be found in the literary and philosophical traditions of pagan cultures are traceable back to the Jewish, Old Testament scriptures, particularly the Pentateuch. To the question, how did pagan poets and philosophers attain to such transcendent truths, Gale answered that they did not attain to those truths, but received them from their source: God, revealing himself in his scriptures to the Jews. Of course, they did not receive the entirety of God’s special revelation to the Jews. Rather they picked up pieces of it here and there. And having received those truths, they, on account of their fallen state, proceeded to corrupt them in their vain imaginations.
“For though [philosophy] were in its origin a weak and imperfect reflexion of that glorious Divine Revelation, which shone from the Son of righteousness on the Jewish church, yet falling on proud, carnal, and indisposed hearts, it did but harden them the more.” Therefore, pagan philosophy, though it had its source and origin in the revelation given to the Jews, became in its subsequent development, a “degenerate, corrupt, and deformed idea, or visage.” (Part III, bk. I, ch. 1, sec. 1; p. 2).
So, volumes one and two are taken up with an elaborate history of the ancient, pagan civilizations’ literary and philosophical traditions, each of which is traced back to interactions with the Israelite people and culture, from which they took away at least some weak and imperfect reflection of divine special revelation. Each volume attempts to elucidate the corruptions that subsequently befell those divine truths in the developments of those pagan traditions.
But the corruptions did not simply befall the pagan traditions. Like as divinely revealed notions worked their way from Jewish literature and culture into that of the pagans, so too then did the corrupted human notions work their way back into the Christian church. In the third volume, Gale attempts to show the ways in which pagan philosophy had been the cause of “antichristianisme” in the various periods of the church, early and medieval. He does not argue that the church was only corrupted in those periods, but rather that corruption had crept in time and again, and caused varying degrees of damage.
And so, in the fourth and final volume, Gale outlines a “reformed philosophie,” (which in the hands of Gale turns out to be a “reduced” and “more sane” platonic philosophy in opposition to the Aristotelianism of the scholastic tradition).
Intra-Reformed debates about a kind of renaissance new Platonism (Cambridge Platonists) and a reformed scholastic Aristotelianism aside, Gales’s overall argument about the fount of pagan natural theology was not unpopular. Other British Protestants had made the case similarly (for example, John Owen’s 1661 Theologoumena Pantodapa, which Gale relies upon throughout).
What this line of argument reveals is that at least some of the Reformed orthodox tackled the perennial question of pagan theological truths in a way that aligned with their understanding of the function of sola scriptura. They were concerned that reason be understood within the bounds of a two-fold limit, finitude and corruption. Though God’s natural revelation goes out to the nations, the light of reason cannot by that revelation ascend to the mysteries of the Christian faith. And, now fallen, what can be known of God even in that natural revelation is by us corrupted. So how to account for those instances where non-Christian writers write sublime truth about God and the world he has made? According to some of the Reformed, these can only be traced back to God’s special revelation.
 The matter is more complicated than I have put it here. The principium essendi, the source of the being of theology (or, we might say the ‘existence’ of theology, but there is further complication with the introduction of this term; what the Reformed, following the medieval scholastic tradition had in mind by essendi, is the coming together of the nature of a thing with the act of existence), the source of the being of theology is God himself. So it is also with the object of metaphysics, whether that be considered God himself or being as common. This more technical side of the discussion need not be explored here. The point here is to say that with respect to the principium essendi, metaphysics and theology have the same source, but with respect to the principium congnoscendi, theology and metaphysics differ.
 The original title is: ΘΕΟΛΟΓΟΜΕΝΑ ΠΑΝΤΟΔΑΠΑ, sive, De natura, ortu, progressu, et studio, veræ theologiæ, libri sex. This work was translated by Stephen Wescott into English under the title Biblical Theology by Soli Deo Gloria Publications in 1994. As the title indicates, however, and by the author’s own admission, this is a rather loose translation, which does not always convey the technicality of its Latin scholasticism. Rather than Biblical Theology, Owen’s original title should be rendered: Various Principles of Theological Method, or, Concerning the Study of True Theology, its Nature, Emergence, and Development.