God’s people are as precious metals, afflictions are His furnace, purification is His design. He therefore puts them into the furnace, and He keeps them there until His end is accomplished. But He supervises the whole process Himself: He regulates the heat, watches its operation, and sits awaiting the fulfillment of His design. He will not be disappointed, for if one affliction does not produce the desired end He sends another.–Daily Remembrancer November 11 Evening
This purging and purifying the author here speaks of is personal. A Christian’s life is not smooth. If it was then Satan has us exactly where he wants us. But God uses the devil as an agent for His own good.