21:1 Sovereignty of God. A king’s decisions are controlled by God. The verse uses synthetic parallelism to develop the point. The first line affirms that the decisions (“heart”) of the king are under the Lord’s control (“in the hand”), and the second explains that God directs the king as he pleases. What clarifies the second line is the simile that the heart is “like a watercourse.” As a farmer channels the water where he wants and regulates its flow, so does the Lord with the king. No human ruler is supreme; to put it another way, the Lord is truly the King of kings. Scripture offers many examples of the truth of this proverb (Ezr 7:21; Isa 10:6–7; 41:2–4; Da 2:21; Jn 19:11).
The Expositor’s Bible Commentary
21:1 He turns it. See notes on 16:1, 9, 33; cf. 19:21; 20:24. Note the examples of the divine hand of God in the cases of Artaxerxes (Ezr 7:21–23), Tiglath-pileser (Is 10:5–7), Cyrus (Is 45:1–4), and Nebuchadnezzar (Da 4:34) and Belshazzar (Da 5:23–25).
MacArthur Study Bible
21:1 The stream of water describes water flowing through a channel or an irrigation ditch, which a skillful farmer can turn to flow wherever he wishes.
ESV Study Bible
21:1 in the hand of Yahweh Even though kings hold great power (Prov 14:28; 16:15; 20:2), they are ultimately under the jurisdiction of God’s power over the entire earth.
Faithlife Study Bible
21:1 The king’s heart … Lord. Possibly a reference to the sovereignty of God even over pagan kings who unwittingly do His will (e.g., Cyrus in Is. 45:1), or to the king of Israel, who, like Solomon, received a special endowment of the wisdom of God (16:10 and note).
Reformation Study Bible