“The crucible is for refining silver and the furnace is for gold, likewise the Lord tests hearts.”
What the Lord does in the life of his saints is similiar to the refining fire, to separate impurities in the heart from what is precious to him. The verse urges cooperation with this process.
How is the Lord testing my heart? What moments and situations is he using to purify my heart? How can I best cooperate with his testing?