Albert Barnes Commentary Proverbs 21:1

"The king`s heart is in the hand of Jehovah as the watercourses: He turneth it whithersoever he will." — Proverbs 21:1 (ASV)

Rivers of water - See the Psalms 1:3 note. As the cultivator directs the stream into the channels where it is most wanted, so Yahweh directs the thoughts of the true king, that his favors may fall, not at random, but in harmony with a divine order.