I used to think doubt was the opposite of faith, that the two stood at opposite ends of a single line, and that growing in one meant shrinking in the other. Now I think doubt is something faith does. A faith with no doubt in it is usually a faith that has simply stopped asking questions.
Part of my confusion was that I had mistaken faith for certainty. They are not the same thing, and I suspect they are closer to opposites. Certainty is a closed hand; it has the answer and no longer needs to look. Faith is an open one, it commits without proof, it trusts in the dark, it keeps walking down a road whose end it cannot see. You do not need faith to believe what you can verify. Faith is the thing you bring precisely where certainty runs out.
The people I find most credible on this are not the ones who never struggled. They are the ones who struggled openly and stayed. When Mother Teresa's letters were published and it turned out she had spent decades feeling that God was silent and absent, some readers took it as exposure, proof that her faith had been a performance. I read it as the opposite. She kept going, in the dark, for fifty years, with no felt reassurance. That is not the absence of faith. That is about as much of it as a person can hold.
The mystics seem to have known this territory well. They gave it a name, the dark night, and treated it not as a failure to be fixed but as a passage to be endured, even a necessary one. Something about the consolation has to be taken away so that what remains is not just the warm feeling of belief but the deeper, colder commitment underneath it. I do not pretend to have traveled far into that country. But I have seen its edges, and I no longer assume that the absence of certainty means the absence of God.
What doubt does, when I let it, is keep my faith honest. It burns off the easy answers, the slogans I reach for when I am not really thinking. It will not let me settle for a god small enough to be certain about. Every time I am sure I have it figured out, doubt arrives like a good and uncomfortable friend and asks the question I was hoping to avoid, and the faith that survives that questioning is sturdier than the one that went in.
So I have stopped trying to win the argument with my own doubt, and started trying to hold the question open without needing to slam it shut. To believe and to wonder at the same time. To say, with the man in the old story, that I believe, and in the same breath to ask for help with my unbelief. I have come to think that sentence is not a contradiction. It may be the most honest prayer there is.