I will first give my reading of the passage, and then explain how it connects with William James' notion of over-belief. (The term 'over-belief' surfaces first in Matthew Arnold who supposedly derives it from Goethe's use of Aberglaube. My concern is solely with James' use of the word, a use to be explained shortly.)
The Pauline Passage
Rather than quote the whole of Romans 1: 18-20, I'll summarize it. Men are godless and wicked and suppress the truth. What may be known about God is plain to them because God has made it plain to them. Human beings have no excuse for their unbelief. "For since the creation of the world, God's invisible qualities — his eternal power and divine nature — have been clearly seen, being understood from what has been made . . . ."
Paul's claim here is that the existence and nature of God are evident from creation and that unbelief is a result of a willful turning away from the truth. There is no excuse for unbelief because it is a plain fact that the natural world is divine handiwork. Now I am a theist and I am sympathetic to Christianity. But although I have one foot in Jerusalem, the other is planted firmly in Athens. And so I must point out that to characterize the natural world as 'made' or 'created' begs the question in favor of theism. As begging the question, the Pauline claim about the evidentness of the world's being created offers no support for theism. If Paul is giving an argument in the passage in question, it is not a good argument. It is an analytic proposition that there is no creation without a creator. So if the heavens and the earth are a creation, then it follows straightaway that a creator exists.
But is the world a divine creation? This is the question, and the answer is not obvious. That the natural world is a divine artifact is not evident to the senses, or to reason. Of course, one can argue for the existence of God from the existence and order of the natural world. I have done it myself. (See my “From Facts to God: An onto-cosmological argument,” International Journal for Philosophy of Religion 48: 157-181, 2000) But those who reject theistic arguments, and construct anti-theistic arguments, have their reasons too, and it cannot fairly be said that what animates the best of them is a stubborn and prideful refusal to submit to a truth that is evident. It is simply not evident to the senses or to reason that the natural world is a divine artifact.
I may be moved to marvel at "the starry skies above me." This was one of two things that filled Immanuel Kant with wonder, the other being "the moral law within me." But seeing as is not seeing. If you see the starry skies as divine handiwork, then this is an interpretation from within a theistic framework, a framework or conceptual scheme that you have superimposed on the data of the senses. But the data can just as easily be given a nontheistic interpretation. Bertrand Russell saw the same starry skies and the universe at large as “just there,” as a brute fact without cause or reason as he said in his famous BBC debate with the Jesuit F. C. Copleston. One and the same datum; two different mutually exclusive interpretations.
If the atheism of some has its psychological origin in pride, stubbornness and a willful refusal to recognize any power or authority beyond oneself, or beyond the human, as is plainly the case with many, it does not follow that the atheism of all has this origin. Not every atheist is of the tribe of Jean-Paul Sartre or Christopher Hitchens.
It is all-too-human to suspect in our opponents moral depravity when we cannot convince them. The Pauline passage smacks of that all-too-humanity — and of the fallacy of psychologism. There are sincere and decent atheists, and they have plenty of excuse for their unbelief. The best of them, if wrong in the end, are excusably wrong. They cannot be dismissed by cheap psychologizing.
Over-Belief in the Pauline Passage
Here is my working definition of 'over-belief' based on my reading of William James: an over-belief is a belief arrived at by reading out of an experience more than is contained within it.
We experience the world as existent, as beautiful, and as orderly. But we cannot conclusively infer that the world is divine handiwork any more than we can conclusively infer that it is a brute fact, that is, a fact without cause, reason, or purpose. That the world is divine handiwork is therefore, by the above definition, an over-belief. But the same goes for the Russellian view that the world is a brute fact. It too is an over-belief.
That is not to say that either view is false. It is to say that both views are undetermined by experience. Over-beliefs are undetermined by what we actually and literally experience. (Admittedly, it is a tricky question what exactly we literally experience: do I see my car, or only the front of my car? Do I touch my cat, or only the fur of my cat? I see a green tree, but do I literally see (with my eyes) that a tree is green? To pursue these questions would take us far afield.)
That the world is divine handiwork is an over-belief. That doesn't make it false or even unreasonable. It is not unreasonable to take the existence, beauty, and order of the world as pointing beyond it to a divine source of its existence, beauty, and order. And because it is not unreasonable, we are within our epistemic rights to supplement what we can legitimately claim to know by faith, which goes beyond what we can legitimately claim to know.
Indeed, over-beliefs are unavoidable. As James writes,
These ideas [over-beliefs] will thus be essential to that individual's religion; — which is as much as to say that over-beliefs in various directions are absolutely indispensable, and that we should treat them with tenderness and tolerance so long as they are not intolerant themselves. As I have elsewhere written, the most interesting and valuable things about a man are usually his over-beliefs. (The Varieties of Religious Experience, Penguin 1982, p. 515, orig. publ. 1902)