J. Gresham Machen, at this point in my life, is probably my favorite author. Last year around this time I read his book Christianity and Liberalism. It was great. The purpose of his book was to identify liberalism (Liberal Christianity) and Christianity (Christianity that holds to the historic Christian doctrines) as two distinct religions. At one point in the book he states,
Admitting that scientific objections may arise against the particularities of the Christian religion . . . the liberal theologian seeks to rescue certain of the general principles of religion, of which these particularities are thought to be mere temporary symbols, and these general principles he regards as constituting “the essence of Christianity.” . . . As a matter of fact . . . what the liberal theologian has retained after abandoning to the enemy one Christian doctrine after another is not Christianity at all, but a religion so entirely different as to belong in a distinct category.
In a previous post, I made a paper I wrote last semester for Ethics class entiled 

In order for Fundamentalism to survive as true historic Fundamentalism, the belief in and defense of fundamental doctrines that are essential to the Christian faith, we have noted so far that Fundamentalism must embrace criticism, recognize it is in a fight for survival against internal problems, and become willing to positively critique itself for the purpose of improvement. With that said, my second “must do” for Fundamentalism is really just a branch off of that first criticism.