Let's review the Stages view briefly, confining ourselves to its attitude toward Christianity. Stage One is the condition of: "God said it; I believe it; and that settles it." Very little room for discussion there. Stage Two urges such arguments as: Everything that exists must have a cause for its existence. Nothing can be its own cause. We either have an infinite regress of causes and effects, or a First Cause. An infinite regress of causes and effects is impossible; consequently there must be a First Cause, and this we call God. (This is the nuts and bolts of the cosmological argument--see St. Thomas Aquinas, the Five Ways.) Much more room for discussion ... of why the argument doesn't work.
Stage Three--Auguste Comte's stage, the pinnacle of the Law of the Three Stages as he saw it--argues against the credibility of Christianity far more than for it. Stage Three, remember, emphasizes scientific observation and hypothetico-deductive reasoning as providing the foundation of our knowledge of the world. It respects Occam's Razor: do not multiply explanations beyond necessity (or: the structurally simplest explanation tends to be the right one). So when Stage Three Thinkers look at what came before, they immediately see the quantum logical leap from the First Cause of Aristotle and Aquinas to the Christian God. All such supposed proofs fail. We can only say, with Stage Three, there's no proof. Science alone has given us no reason to believe there are any gods or other supernatural agencies. Why not simply become an agnostic? Why not become a Humanist--who begins ethics from a human perspective rather than basing its view of the universe on a deity who probably does not exist.
Consider, though: there are many forms Humanism can take, because there are many possible human starting points for painting a moral picture of the world. Do we rest on human reason, as Kant did? Do we rest on our pursuit of pleasure and avoidance of pain, and for the greater number, as Bentham did? Do we urge pursuing the greatest happiness for the greatest number, as Mill did? Or, finally, do we become rational ethical egoists, as Ayn Rand did and as many Libertarians have done? All of these ethical theories have well-drawn drawbacks. Christian ethics is surely no worse off than the utilitarian theory that is fully consistent with, e.g., the Tuskegee Experiment.
Stage Four (postmodernism) sees this multiplicity--no different fundamentally than the multiplicity of religions in the world--and wonders what it means to be a Humanist.
A possible view at the end of the road for both Stage Three and Stage Four thinkers is that morality is simply a delusion. What happens is that the strongest or most conniving (or both) rule over the rest, that it has always been that way and always will be as long as there is a human race. Many of us have become convinced over the years that this is, indeed, the most direct consequence of materialism (the view that reality consists exclusively of physical or material reality). Now it is true that we can work within this kind of perspective to improve lives--our own and those of others. We can make as many people as possible comfortable, if we are willing to do what is necessary, and we are drifting back toward utilitarianism again--although it will be a utilitarianism for the common man who never peers behind the curtain and looks for fundamental justifications. The philosopher will know better. The philosopher peers behind the curtain, and what he sees is a fundamental amoralism, which the Humanist perspective papers over.
So then what of Fifth Stage belief? At what point is God recovered, and why--especially if Stage Five Thinkers essentially agree that the arguments for God's existence all fail, adding that such arguments were never a good idea in the first place. How does Stage Five transcend Stage Four? Have we ever clearly characterized Civilization's Fifth Stage???
These are crucial questions to be taken up and responded to over time. The first thing to note is that an incipient Fifth Stage exists today in the writings both of systems thinkers (who seldom address theological matters) and of reformed theologians such as Cornelius Van Til whose theism is informed and sharpened through the contrast with its opposition. Presuppositionalism, at the start, is the idea that we never approach the world from a purely objective perspective, if by objective we mean entirely neutral. We begin, instead, with presuppositions about the world we wish to understand: either it is ordered or it is possibly chaotic with order an illusion; either it is knowable in essence, at least in part, or we give up the search for truth as postmodernists recommend. And we presuppose that morality means something, that it is not a mere delusion that captivates those of us who have moral compasses, however imperfect.
In that case, why is reality ordered and not simply chaotic; how are explanations possible at all (a transcendental question)? The philosopher does not deny science; he does not deny that explanations--very detailed ones--have been given for a wide variety of natural phenomena. He notes that in a chaotic universe, life would probably be impossible. In our universe, life flourishes and solves problems with efficiency and enthusiasm. Technology embodies our successes at understanding and mastering important domains of our experience, up to a point. What the philosopher does not want to do is stop at the brute facts of successful explanation and successful problem solving.
After all, to the postmodernist, it is all an illusion. The Stage Four Thinker cannot account for successful scientific explanation and its myriad technological applications. He cannot account for our knowledge of them, or assure us that even if our knowledge of them is, at present, stable, it will remain such. After all--as David Hume was the first to note--it is logically possible, given experience as a stream of impressions, logic as relations of ideas, and nothing more, that all of nature's laws will change at some point in the future. Our claims of universal knowledge of nature's laws will have been shown to be a deception, as is our supposed mastery of our surroundings (which may turn out to be illusory for quite different reasons!).
Now suppose a Creator really does exist, after all. Suppose, moreover, this Creator both created a universe--or physical reality--of order and not chaos. Suppose, furthermore, the Creator fashioned us with minds and senses structured so as to apprehend those aspects of physical reality most likely to assure our ability to survive and prosper in physical reality assuming we use our minds and senses. Now if this Creator of a certain type--supremely rational, at the very least--both exists and accomplished these things, we have at hand explanations for (a) the orderly nature of physical reality, even if we haven't grasped every aspect of this order; (b) the fact that we can reliably apprehend physical reality, at least in part, in order to solve myriad human problems, and finally (c) we have an explanation for whatever moral compass exists within ourselves, quite independent of any holy book such as the Bible, that tells us, You should do better. For a fallen race can still understand the difference between right and wrong. The fact that we speak clearly of sociopaths as lacking such a compass is telling. It is evidence that the majority of us have one.
The Christian Presuppositionalist, in this case, sees God as both metaphysical and epistemological foundation, though not quite in the sense of the foundations of Descartes or Kant. They thought they were providing decisive proofs. The Christian Presuppositionalist harbors no such illusions. He is informed by the perspectives of the agnostic and the atheist, remember. He believes that their explanations of the world and of knowledge seem good at first glance but disintegrate under close analysis and end up leaving us completely at sea.
The agnostic and atheist disagree, of course. They believe they have explanations of how the universe and life arrived at its present state--in essence, aside from any number of missing details. They believe we don't need to posit a God. Many of their explanations, in so far as they are confined to physical reality, are quite good. But they ignore one important factor: they have not told us how explanations are possible. Stage Three Thinkers, I submit, bypassed this query as "too metaphysical"; Stage Four Thinkers then doubted that they really are possible! A Stage Five Thinker then might respond with the transcendental argument outlined above. He will claim that the very existence of successful explanations presupposes God--as the Supreme Logos.
He will acknowledge that this isn't a proof.
He will acknowledge that others might disagree.
He will acknowledge that he is saying, in effect, "These are my presuppositions. This is where I take my stand. This is where my best human logic seems to have taken me."
He will allow those unconvinced to go their own ways in peace. He does believe we should keep talking to each other despite our disagreements, because there are many problems of civilization we can still work together on. Here is the Stage Five Thinker's concrete difference from the Stage One Thinker. The latter is a theocrat at heart. The Stage Five Thinker is, in my considered opinion, fundamentally a libertarian.