This essay is essential reading, and is timeless. Here is a good example of its power.
“If we are really convinced of the truth of our message, then we can proclaim it before a world of enemies, then the very difficulty of our task, the very scarcity of our allies becomes an inspiration, then we can even rejoice that God did not place us in an easy age, but in a time of doubt and perplexity and battle. Then, too, we shall not be afraid to call forth other soldiers into the conflict. Instead of making our theological seminaries merely centres of religious emotion, we shall make them battle-grounds of the faith, where, helped a little by the experience of Christian teachers, men are taught to fight their own battle, where they come to appreciate the real strength of the adversary and in the hard school of intellectual struggle learn to substitute for the unthinking faith of childhood the profound convictions of full-grown men.”
-J. Gresham Machen, “Christianity and Culture,” 1912 (emphasis mine)
The essay in its entirety can be found here: http://www.marshillaudio.org/pdf/documents/ChristianityCulture.pdf