Matthew Henry and continuators on Proverbs 17:3

3 The fining pot is for silver, and the furnace for gold: but the Lord trieth the hearts.

Note, 1. The hearts of the children of men are subject, not only to God's view, but to his judgment: As the fining-pot is for silver, both to prove it and to improve it so the Lord tries the hearts; he searches whether they are standard or no, and those that are he refines and makes purer, Jer. xvii. 10. God tries the heart by affliction (Ps. lxvi. 10, 11), and often chooses his people in that furnace (Isa. xlviii. 10) and makes them choice. 2. It is God only that tries the hearts. Men may try their silver and gold with the fining-pot and the furnace, but they have no such way of trying one another's hearts; God only does that, who is both the searcher and the sovereign of the heart.