Rob Bell:

For many people in our world, the opposite of faith is doubt.  The goal, then, within this understanding, is to eliminate doubt.  But faith and doubt aren't opposites.  Doubt is often a sign that your faith has a pulse, that it's alive and well and exploring and searching.  Faith and doubt aren't opposites; they are, it turns out, excellent dance partners.

What We Talk About When We Talk About God, p. 92