The problem, therefore, is the recognition of that spiritual principle which, as impelling force, lies at the base of the entire sum and series of historical religious phenomena, and is expressed most imperfectly in the lowest stages, most purely and completely in the highest stages of the religious experience — that is to say, in Christianity. We may not, however, conclude from this that the essence of religion exactly corresponds to historical Christianity — that an historically reached definition of Christianity would at the same time serve as a definition of religion. Nor is the philosopher of religion thereby excused from further attempts to investigate religion. Various reasons forbid such a contraction of the philosopher's field of vision. As Christians we may be fully convinced that Christianity is the most perfect religion; yet the philosopher cannot assume this as an unproved postulate, but must seek to justify the conviction. This can be done only by comparing Christianity with other religions. Evidence must be brought from the history of the development of religions, that the other religions serve Christianity as a preparation, as subordinate stages, or that they contain only particular phases of religion, which are realized in Christianity in a higher and more comprehensive manner. It is clear, however, that such a comparative view of religions is impossible without some criterion. Now no historically given fact can furnish such a criterion, for this itself must be subjected to criticism. Nor is the universal concept of religion arrived at by induction a suitable criterion, for its content would be much too indefinite to furnish judgments concerning the relative worth of religions. If, however, we cannot obtain from history the norm necessary to an evaluation of religions, we must seek it within the religious self-consciousness itself. Of course it does not exist there as an 'innate idea,' for there are no 'innate ideas.' The religious idea manifests itself within us as an impellent force and craving, whose realization and satisfaction are reached through the interaction between this consciousness and its historical environment. The co-operation and harmony of these two factors — the natural predisposition and the external influences — bears witness to
