[On the supposed inability of the Reformers to transcend the medieval natural/ supernatural dichotomy concerning revelation] As a result, reason again achieved some measure of authority alongside of faith. It seemed reason did not always have to be guided by faith and was in fact, be it in an ever so small and indifferent area of life, free and independent. With this right being granted to it—at least not seriously contested—reason turned to its own advantage and gradually expanded its domain. First in civil matters, then in science, soon also in philosophy reason elevated itself to a position alongside of and over against faith. Alsted, who published an independent "natural theology" ... Many Reformed theologians followed suit, especially when Cartesian philosophy gained more influence.
As a result of English deism and German rationalism, "natural" or "rational" theology so increased in power and prestige that it rejected revealed religion as totally unnecessary. ... But after it had banished revealed theology, natural theology was itself judged in turn. [Immanuel] Kant asserted in his Critique of Pure Reason that the latter is restricted to phenomena of sense perception and can neither penetrate to the supersensible nor to the supernatural. ... [Herman Bavinck, Reformed Dogmatics, 1:306]
It seems that Herman Bavinck is asserting that the focus on natural theology (as opposed to a supernatural theology of nature) leads one to (capital "r") Rationalism and the destruction of the faith.