Historically the study of religion has been subsumed under the headings of anthropology, sociology, or even psychology. The academic investigation of religion has sought to be grounded in a scientific-empirical method. The reason for this is quite simple. Human activity is part of the phenomenal world. It is activity that is visible, subject to empirical analysis. Psychology may not be as concrete as biology, but human behavior in response to beliefs, urges, opinions, and so forth can be studied in accordance with the scientific method. To state it more simply, the study of religion is chiefly the study of a certain kind of human behavior, be it under the rubric of anthropology, sociology, or psychology. The study of theology, on the other hand, is the study of God. Religion is anthropocentric; theology is theocentric. The difference between religion and theology is ultimately the difference between God and man—hardly a small difference.
Grace Unknown, The Heart of Reformed Theology