Doubt

If we have never doubted, how can we say we have really believed? True belief is not about blind submission. It is about open-eyed acceptance, and acceptance requires persistent distance from the truth, and that distance is doubt. Doubt, in other words, can feed faith, rather than destroy it. And it forces us, even while believing, to recognize our fundamental duty with respect to God's truth: humility. We do not know. Which is why we believe.

--Andrew Sullivan