From Trusting God Even When Life Hurts, by Jerry Bridges
God disciplines us with reluctance, though He does it faithfully. He does not delight in our adversities, but He will not spare us that which we need to grow more and more into the likeness of His Son. It is our imperfect spiritual condition that makes discipline necessary.
This is not to say that every adversity that occurs in our lives is related to some specific sin we have committed. The issue God is dealing with in our lives is not so much what we do, but what we are. All of us tend to underestimate the remaining sinfulness in our hearts. We fail to see the extent of pride, fleshly self-confidence, selfish ambitions, stubbornness, self-justification, lack of love, and distrust of God that He does see. But adversity brings these sinful dispositions to the surface just as the refiner's fire brings impurities to the surface of the molten gold.