Just as courage is persisting in the face of fear, so faith is persisting in the presence of doubt. Faith becomes then a commitment, a practice and a pact that is usually sustained by belief. But doubt is not just a roiling, or a vulnerability; it can also be a strength. Doubt acknowledges our own limitations and confirms — or challenges — fundamental beliefs, and is not a detractor of belief but a crucial part of it.

As Christopher Lane argued in “The Age of Doubt,” the explosion of questioning among Christian thinkers in the Victorian era transformed the idea of doubt from a sin or lapse to necessary exploration. Many influential Christian writers, like Calvin and C.S. Lewis, have acknowledged times of uncertainty. The Southern writer Flannery O’Connor said there was “no suffering greater than what is caused by the doubts of those who want to believe,” but for her, these torments were “the process by which faith is deepened.”

Mother Teresa, too, startled the world when her posthumous diaries revealed that she was tormented by a continual gloom and aching to see, or sense, God. In 1953 she wrote, “Please pray specially for me that I may not spoil His work and that Our Lord may show Himself — for there is such terrible darkness within me, as if everything was dead. It has been like this more or less from the time I started ‘the work.”’

And yet by this work, she helped many thousands of people.