Christianity certainly did not just “grow up”; it was founded. And subsequently to its founding, it has not “run wild,” gone off in this or that direction according as some contentless “informing spirit” or “germinal life” within it may have chanced to lead it; it has been held strictly, more strictly than any other religious movement, to its fundamental type, by constant references back to its foundations. For whatever reason, on whatever ground, it has kept a constant check upon itself lest it should depart from type, and has shown an amazing power, after whatever aberrations, continually to return to type. Its eye has been fixed not merely in forward gaze but in backward as well. It has manifested a unique capacity of growth, justifying its Founder’s comparison of it to the mustard-seed and to the leaven; but, after all is said as to the transformations it has suffered, its slacknesses, its degenerations, its failures, its growth has lain not in the gradual development of a content for itself, but in the steadily increasing assimilation of its environment to itself. – B.B. Warfield in The Essence of Christianity