I'll save the reader the predictable and trite interpretation of this rich tale in the interest of a more subtle point or two.

By the time he met the giant, David had already battled the lion.  David had called upon his spiritual resources for the battle and in so doing, had gained familiarity with the power which was available to him.

By the time he met the giant, David had already battled the bear.  Again, David had called upon his spiritual resources for the battle and in so doing, had gained familiarity with the power which was available to him.

And so it is with us.  As we take the time on a regular basis to gain familiarity with the power which is available to us - as we take the time on a regular basis for spiritual practice - we become stronger.  We become well-practiced.  We become like young David - perfectly confident in our power, even in the face of a staggering apparition.

Like young David, we decline the armor and the helmet and the sword.  We know that the power within us far exceeds our personal resources.

You see, David's victory over Goliath wasn't a product of providence.  David's victory over Goliath was a product of practice.

And without that practice, this would have been the story of how David got his ass kicked.