Admittedly, article 2 of the Belgic Confession states that God is known by two means—nature and Scripture—and natural theology is upheld in its truth and value by all Reformed theologians. But in that first period, before rationalism infected Reformed Theology, it was clearly seen that nature and Scripture are not detached and independent entities, any more than natural and revealed theology are. Calvin incorporated natural theology into the body of Christian dogmatics, saying that Scripture was the spectacles by which believers see God more distinctly also in the works of nature. Originally natural theology was by no means intended to pave the way, step by laborious step, for revealed theology. In adopting it, one was not assuming the provisional stance of reason in order next, by reasoning and proof, to mount to the higher level of faith. But from the very outset the dogmatician took a stand on the ground of faith and, as a Christian and believer, now also looked at nature. Then, with his Christian eyes, armed by the Holy Scripture, he also discovered in nature the footprints of the God whom he had come to know—in Christ and by Scripture—as Father. From a subjective point of view, in dogmatics it was not therefore natural reason that first took the floor, after which faith in the Word had its say. On the contrary, it was always the believing Christian who, in catechism, confession, and in dogmatics, gave voice to his faith. And in the same way, speaking objectively, nature did not stand on its own as an independent principle alongside of Holy Scripture, each of the supplying a set of truths of their own. Rather, nature was viewed in the light of Scripture, and Scripture not only contained revealed truth (in the strict sense) but also the truths that a believer can discover in nature. Thus Alsted did indeed acknowledge the existence of a natural theology in the unregenerate, but a confused and obscure natural theology. By contrast, for the believer the principles and conclusions of natural theology are replicated clearly and distinctly in Scripture.
So, though one can speak of a knowledge of God derived from nature, dogmatics still has but one external foundation (principium externum), i.e., Holy Scripture, and similarly only one internal foundation (principium internum), i.e., believing reason. And it is not simply the case that Holy Scripture is only the norm and not he source of dogmatics, but it is specifically the foundation (principium) of theology. Between earlier theologians and those of today there is a major difference. Herman Bavinck, Reformed Dogmatics Prolegomena Vl. I pp. 87,89
There is no such thing as a separate natural theology that could be obtained apart from any revelation solely on the basis of reflective considerations of the universe. The knowledge of God that is gathered up in so-called natural theology is not the product of human reason.
Rather, natural theology presupposes, first of all, that God reveals himself in his handiwork. It is not humans who seek God but God who seeks humans, also by means of his works in nature. That being the case, it further presupposes that it is not humans who, by the natural light of reason, understand and know this revelation of God. Although all pagan religions are positive [concrete], what is needed on the human side is a mind that has been sanctified and eyes that have been opened in order to be able to see God, the true and living God, in his creatures. And even this is not enough. Even Christian believers would not be able to understand God’s revelation in nature and reproduce it accurately had not God himself described in his Word how he revealed himself and what he revealed of himself in the universe as a whole. The natural knowledge of God is incorporated and set forth at length in Scripture itself. Accordingly, Christians follow a completely mistaken method when, in treating natural theology, they, as it were, divest themselves of God’s special revelation in Scripture and the illumination of the Holy Spirit, discuss it apart from any Christian presuppositions, and then move on to special revelation.
Even when Christians do theology, from the very beginning they stand with both feet on the foundation of special revelation. They are Christ-believers not only in the doctrine of Christ but equally in the doctrine of God. Standing on this foundation, they look around themselves, and armed with the spectacles of Holy Scripture, they see in all the world a revelation of the same God they know and confess in Christ as their Father in heaven.
Reformed Dogmatics Vl. 2 pp 74,75