When in the process of historical research the step is taken from a mere collecting of facts to a meaningful interpretation of these facts, we may speak of the maturity of this historical research. If that is true in general history, it is even more significant in the field of church history where ideas and spiritual principles dominate the scene. But the difficulties in this area are even more conspicuous than elsewhere. A perfectly objective church historiography is almost impossible due to the inevitable bias of the writer, his sympathies and his restricted ability to appreciate phenomena in widely different fields. In fact, no historiography can do without a set of categories and concepts of a specific nature, and the choice of these is definitely the work of the particular research person and his preferences.