Update: Some have asked, does this critique of Geisler and Bultmann include a great like C. S. Lewis? To some extent, yes. In Mere Christianity Lewis attempts to justify Christian belief without appeal to revelation. By doing that, he’s following Thomas Aquinas’ second form of theology, that revealed by nature. He does something similar in The Abolition of Man where he appeals to the tao, an objective and universal source of morality. Where I’m unsure is about where Lewis locates belief or faith in the process of knowing.
Methodologically, both Normal Geisler and Rudolf Bultmann appeal to an authority that is higher or more ultimate than the revelation of God in Christ and in Scripture through faith. Both appeal, albeit in different ways, to reason as a neutral arbiter and path to truth (rather than to divine illumination). In this sense then, both are working from a thoroughly modern epistemology–we know through reason and we validate through reason.
Jamie Smith notes, “[The] Thomistic model of the relationship between revelation and reason (and hence grace and nature) informs a diversity of other models, directly or indirectly, ranging from Rudolf Bultmann’s and Paul Tillich’s correlationist theologies to what is often described as classical apologetics in the evangelical tradition. All of these models remain colonies of Tübingen insofar as they concede that there is an objective or neutral reason that determines the shape of truth concerning finite existence and then attempt to demonstrate Christianity’s consistency with this rational account (as in Bultmann and Tillich) or to demonstrate the truth of Christianity’s account by appealing to neutral principles of truth that are common to all humanity (as in classical apologetics).”
James K. A. Smith, Introducing Radical Orthodoxy, 158.
What if secular reason, the neutral reason alluded to in Smith’s description of classical apologetics, does not exist? What if secular reason is, in reality, something that stands in opposition to the Christian gospel as expressed in revelation? What if positing the existence of secular reason was the very philosophical misstep that led to the decline of Christendom and the rise of modernity?
Concludes Smith, “Things are not anything ‘in themselves’; therefore, they cannot be understood ‘in themselves’ but only by reference to that from which they are suspended–their Creator. As a result, no secular account of things could possibly be true.” (160).