Systematic theology is, and of right ought to be, primarily practical. In the first place, true religion is both one of the ends of an ideal human life and, in the long run, an indispensable means to the morality which is most essential to human welfare, inner and outer. In the second place, theology is necessary as an instrument for the proper control of the development and expression of religion—a special case of the function of ideas in the control of life. It follows, therefore, that a sound theology is a human necessity. The purpose of the theologian, whatever else it may or must include, must be to find those religious truths which are essential to the vitality and efficiency of the best type of human religion.

That this has really been the aim of theologians in the great formative periods of the history of Christian doctrine may readily be shown. The prevailing impression with regard to orthodoxy and excluded heresies is that the distinction between them is arbitrary and external. This is indeed to the modern mind true in large measure of the distinction between the old orthodoxy and heresy; but in their own day this distinction was neither arbitrary nor external. Then it was organically related to the most pressing of problems; it was supremely vital, for the issues involved were nothing short of spiritual life and death.