When the film version of C.S. Lewis’s The Chronicles of Narnia debuted in 2005, Joe Sobran wrote:

Belief is something you have or don’t have; but faith is an act of will and fortitude, which is why we speak of “keeping” or “breaking” faith.

A child may know perfectly well that the water is safe and that anyone can learn to swim, but still allow himself to succumb to fear of the water when he actually gets into it. The problem isn’t the child’s “beliefs” about the water; it’s his irrational panic. In the same way, Lewis explains in Christian Reflections, we may believe intellectually, but allow our moods and passions to weaken our faith when we are tempted.

When our faith fails, it isn’t usually because of any rational doubt. Reason isn’t opposed to faith; it’s opposed to the passions (the word is cognate with passive; we’re truly active only when we act rationally). In spite of all the clichés equating intelligence with doubt, the loss of faith doesn’t occur in the intellect, but in the will. Lewis understood this…

When we talk about things like “culture” or “refinement” or “manners” we’re talking at least to some degree about restraining our animalistic passions or inclinations. When laziness overcomes us—when the leather of the couch is warm, and our eyes heavy—we’d much rather not go out. Our reason is overcome, even as it tries to tell us to keep our appointment, or to arrive on time, or whatever. Same with avoiding a workout, and any other dozen instances where a sort of lie (“This other thing would be better for you…”) replaces a truer purpose.

Ben Casnocha introduced me years ago to the idea of a “resilience quotient,” basically meaning fortitude. C.S. Lewis, as Sobran explains it, is arguing similarly about faith in Christ as a means to withstand the vicissitudes of our baser instincts.