For most of Christian history theology was not organized into the departments a modern seminary catalog lists. What changed that was a short handbook, not a doctrinal treatise. In 1811, helping to design the curriculum for the newly founded University of Berlin, Friedrich Schleiermacher wrote the Brief Outline on the Study of Theology, arguing that theology should be organized as a positive science serving the practical needs of a functioning church, and dividing the field into three interlocking branches, philosophical theology examining the concept of Christianity itself, historical theology covering scripture, church history and the present state of doctrine, and practical theology concerned with leading and governing a congregation, with historical theology further split into biblical and church historical study.
The scheme did more than organize one curriculum. Schleiermacher's fourfold shape, usually simplified since to biblical, historical, systematic and practical theology, became the working template for how Protestant and eventually Catholic institutions divide theological education, so that a present day seminary's separate departments for scripture, church history, doctrine and ministry are still, largely without anyone citing him directly, running on Schleiermacher's own answer to a question he was the first to pose formally: not what should theology teach, but what kind of science is theology in the first place, and how many distinct kinds of inquiry does answering that question actually require.