To put it mildly, religion has always been a sensitive subject, and no less so for historians than for anyone else. Throughout human history, the vast majority of people have simply assumed the existence of an unseen realm, that of the gods, the spirits, the sacred, or the Divine. They further accepted the capacity of human beings, guided often by tradition, ritual, or religious authority, to align themselves with that other world. But more recently, as an outgrowth of the Scientific Revolution and the European Enlightenment, some have challenged those assumptions, arguing that the only realities worth considering are those that can be accessed with the techniques of science and our five senses. This situation has generated various tensions or misunderstandings between historians and religious practitioners because modern secular historians, whatever their personal beliefs, can rely only on evidence available in this world.

One of these tensions involves the question of change. Most religions present themselves as timeless revelations from the beyond, partaking of eternity or at least reflecting ancient practice. In the eyes of historians, however, the religious aspect of human life changes as much as any other. The Hindu tradition changed from a religion of ritual and sacrifice to one of devotion and worship. Buddhism became more conventionally religious, with an emphasis on the supernatural, as it evolved from Theravada to Mahayana forms. A male-dominated hierarchical Christian Church, with its pope, bishops, priests, and state support, was very different from the small house churches that suffered persecution by imperial authorities in the early Christian centuries. The implication—that religions are largely a human phenomenon—has been troublesome to some believers.

Historians, on the other hand, have sometimes been uncomfortable in the face of claims by believers that they have actually experienced a divine reality, and therein lies a second problem. How could such experiences be verified, when even the biographical details for Buddha and Jesus are difficult to prove by the standards of historians? Certainly, modern historians are in no position to validate or refute the spiritual claims of these teachers, but we need to take them seriously. Although we will never know precisely what happened to the Buddha as he sat in meditation in northern India or what transpired when Jesus spent forty days in the wilderness, clearly those experiences changed the two men and motivated their subsequent actions. Later, Muhammad likewise claimed to have received revelations from God in the caves outside Mecca. Millions of the followers of these religious leaders have also acted on the basis of what they perceived to be an encounter with the Divine or the unseen. This interior dimension of human experience, though difficult to grasp with any precision and impossible to verify, has been a significant mover and shaper of the historical process.

Yet a third problem arises from debates within particular religious traditions about which group most accurately represents the “real” or authentic version of the faith. Historians usually refuse to take sides in such disputes. They simply notice with interest that most human cultural traditions generate conflicting views, some of which become the basis for serious conflict in societies.

Reconciling personal religious convictions with the perspectives of modern historical scholarship is no easy task. At the very least, all of us can appreciate the immense human effort that has gone into the making of religious traditions, and we can acknowledge the enormous significance of these traditions in the unfolding of the human story. They have shaped the meanings that billions of people over thousands of years have attached to the world they inhabit. These religious traditions have justified the vast social inequalities and oppressive states of human civilizations, but they have also enabled human beings to endure the multiple sufferings that attend human life, and on occasion they have stimulated reform and rebellion. And the religions born in second-wave civilizations have guided much of humankind in our endless efforts to penetrate the mysteries of the world beyond and of the world within.