Christianity and Liberalism by J. Gresham Machen

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.

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