The refining of silver or gold requires an extremely hot fire (around 2,000 degrees Fahrenheit), a craftsman willing to skimming the dross off the top and a rock of silver or gold. In this proverb, it says that the Lord does the same thing to test our hearts.
We are the rock, God Himself is the Craftsman and the circumstance of life is the fire. Challenges come – God is cranking up the furnace. How many impurities will rise to the top? Impurities like unbelief, despair or anger. If success comes (and it can still be the turning up of the heat,) impurities like pride, self-reliance and greed can surface.
May we be sensitive to the heat around us and be willing to allow the impurities to come and when they do, we will allow the Craftsman to skim them off.