It’s probably true that most people would think in terms of opposites here. Most likely, faith would be seen as located on one extreme end of the spectrum, and doubt on the other. Where one exists, the other can’t.
But I don’t think this is the case. It may be more accurate to say that faith and doubt stand side-by-side at one end, and unbelief at the other. Faith and doubt are typically linked together, informing as well as challenging each other, causing faith to grow as doubt spurs it on to greater and greater heights. With each new doubt should come the motivation for more thinking, research, and prayer in order to move forward and upward. With God’s help the new level of faith that emerges from the struggle will be superior to the old.
So doubt, far from being the sinful and destructive thing people tend to think it is, is actually the guard that keeps us from falling asleep. It brings the necessary pressure upon faith to keep it from becoming the mindless “leap-in-the-dark” imaginary thing it’s so commonly accused of being. Doubt poses the perennial questions to faith: Is this actually real and true? Am I trusting in something reliable? Am I being fooled by some clever religious advertising? Is this authentic faith or just religion?
From the struggle these questions create comes the constant working through and strengthening of what we believe.
