In the sphere of religion, in particular, the present time is a time of conflict; the great redemptive religion which has always been known as Christianity is battling against a totally diverse type of religious belief, which is only the more destructive of the Christian faith because it makes use of traditional Christian terminology. This modern non-redemptive religion is called “modernism” or “liberalism.” Both names are unsatisfactory; the latter, in particular, is question-begging. The movement designated as “liberalism” is regarded as “liberal” only by its friends; to its opponents it seems to involve a narrow ignoring of many relevant facts. And indeed the movement is so various in its manifestations that one may almost despair of finding any common name which will apply to all its forms. But manifold as are the forms in which the movement appears, the root of the movement is one; the many varieties of modern liberal religion are rooted in naturalism–that is, in the denial of any entrance of the creative power of God (as distinguished from the ordinary course of nature) in connection with the origin of Christianity. The word “naturalism” is here used in a sense somewhat different from its philosophical meaning. In this non-philosophical sense it describes with fair accuracy the real root of what is called, by what may turn out to be a degradation of an originally noble word, “liberal” religion.
Machen’s book is an important text that belongs in every theological library. A decade ago I taught a course on Heresy at Tyndale Theological Seminary and used Christianity and Liberalism as one of the required texts. The other required text was Harold O.J. Brown’s book Heresies: Heresy and Orthodoxy in the History of the Church.