Theological liberalism is an attempt to modernize the Christian faith and “bring it up to the times.” At the turn of the 20th century, this often took the shape of folks denying things like Christ’s bodily resurrection or the virgin birth. Today it might take the form of certain churches wanting to revise the Bible’s teaching on sexual ethics. But in both cases, the strategy is to save Christianity by making it more acceptable to culture. In this classic from 1923, J. Gresham Machen argues that such theological liberalism is not merely a new approach to Christianity; instead, it’s not Christianity at all.