The Lord weighs the heart.
v.1 Stream of water. The king’s heart is like a stream of water that the Lord turns wherever he wills. Example in Ezr 6:22. Illustrates the sovereignty of God.
v.2 Way of a man. The ways of a man seem right in his own eyes, but the Lord weights the heart (to see motives). Repeated from 16:2.
v.3 Righteousness and justice. Righteousness and justice are more pleasing to the Lord than sacrifices. See Ps 40:6-8 and Mi 6:6-8. Godly actions flow from a godly heart.

Read Proverbs 21:1-3