Having served as an infantryman during World War I, Lewis had first-hand experience of battle. What’s more, much of Mere Christianity originally took the form of radio addresses delivered to the British public in the midst of World War II. It is therefore not surprising that Lewis often reaches for the language of warfare and combat to describe the Christian life—and, in particular, the conflict between good and evil—to his audience. Here, for instance, is Lewis’s account of humanity’s fallen nature: “[F]allen man is not simply an imperfect creature who needs improvement: he is a rebel who must lay down arms” (56).

Of course, this kind of rhetoric is not unique to Lewis, though he often gives it a more modern twist, as when he talks about listening to a “secret wireless” in church (46). In fact, not only has militaristic language permeated Christian writings, it has shaped Christian practice in the form of historical events like the Crusades. However, this raises an important point: The Crusades (and in fact war in general) were filled with acts that seem deeply un-Christian. In fact, some Christians would argue that the Bible prohibits killing at all.