Doubt

(George MacDonald - found here)

“To deny the existence of God may ... involve less unbelief than the smallest yielding to doubt of His goodness. I say yielding; for a man may be haunted with doubts, and only grow thereby in faith. Doubts are the messengers of the Living One to the honest. They are the first knock at our door of things that are not yet, but have to be, understood.... Doubt must precede every deeper assurance; for uncertainties are what we first see when we look into a region hitherto unknown, unexplored, unannexed.”

~George MacDonald