Theology is the study of a religious tradition.
It can embrace the history of literature in that tradition, the study of institutions, the history of the political causes and effects of religious movements and the philosophical scrutiny of their claims about God and the world. It is primarily the study of the Christian tradition from the Bible to the present day, leaving students free to decide whether they wish to concentrate on philosophical or historical questions. The Old Testament, the New Testament, the early Church to 451 A.D., twentieth-century doctrine. Each of these subjects can be pursued further, e.g. by learning a relevant languages, by studying extra texts, by choosing a particular theologian to work on, by doing separate papers on doctrine and history of the same period. Yes, if you think it's narrow to study the most important influence on the last 2000 years of world history.