RC Sproul tells this story:
Several years ago I was invited to address the faculty of a prominent Midwestern college with a rich Christian and Reformed tradition… Before my lecture the dean showed me around the campus. When we entered the faculty office building, I noticed one office with these words stencilled on the door: Department of Religion. That evening as I spoke to the faculty, I [asked]… “Was that department always called the Department of Religion?” My inquiry was greeted by silence and blank stares… Finally an elder statesman of the faculty raised his hand and said, “No, it used to be called the Department of Theology. We changed it about 30 years ago.” “Why did you change it?” I asked. No one in the room had any idea, nor did they seem to care… I reminded the faculty that there is a profound difference between the study of theology and the study of religion. Historically the study of religion has been subsumed under the headings of anthropology, sociology, or even psychology… [T]he study of religion is chiefly the study of a certain kind of human behavior… The study of theology, on the other hand, is the study of God… The difference between religion and theology is ultimately the difference between God and man– hardly a small difference… The subject matter of theology propoer is God; the subject matter of religion is man.
To put it another way, religion looks at the beam, theology looks along the beam.