Bridges on Proverbs 21:1
Charles Bridges on Proverbs 21:1

1.  The king’s heart is in the hand of the LORD, as the rivers of water: he turneth it whithersoever he will.
MOST reflecting persons acknowledge God as the doer of all things. In inert matter he acts by physical force; in brute animals, by instinct and appetite; in intelligent beings, by motives suited to their faculties; in his redeemed people, by the influence of grace. We are here reminded of one course of his Providential acting. The general truth, before stated, of man’s entire dependence, is taught by the strongest illustration — his uncontrollable sway upon the most absolute of all wills — the king’s heart.
The river of water is an apt emblem of this agency. Its commencement is a single spring; scarcely capable of turning an handmill to grind a day’s corn. But increased by the confluence of other small or great streams, it may turn hundreds of mills, and provide food for thousands. So the thoughts of the king’s heart are first a single imagination for the good of his subjects; then swelled by the attendant thoughts of his mental resources, till what appeared desirable rises to the full power of accomplishment. But after all, the Great Sovereign turns the most despotic rule, all political projects, to his own purposes, with the same ease, that the rivers of water are turned by every inflection of the channel.† While this course is directed, the waters flow naturally and unforced on their own level. The king’s heart he directs as a responsible agent, without interfering with the moral liberty of his will.
Nehemiah fully acknowledged this prerogative, when, having a favor to ask of the king, he “prayed unto the God of heaven.”† And indeed Scripture witness is abundant. Abimelech’s heart was in the hand of the LORD for good.† Pharaoh’s heart was turned towards Joseph.† The Babylonish monarchs showed kindness to Daniel and his captive brethren.† The Persian monarchs countenanced and assisted in the building of the temple.† The hearts of wicked kings are alike in the hand of the LORD; † yet he hath no part in their wickedness.† The hatred of Pharaoh; the ambition of Sennacherib and Nebuchadnezzar,† were his instruments for his own purposes. Ahab’s murderous heart was restrained, and even made to accomplish the downfall of Baal.† The counsels of the kings of the earth against Christ were under Divine control.† Thus does “the wrath of man praise him; and the remainder he restrains.”† Thus an Almighty agency is visible by its effects in the minutest affairs. Ahasuerus’s sleepless nights;† Nebuchadnezzar’s divination;† the appointment of the year of general taxation† — these seemingly unimportant events were turning-points in the dispensations of God, fraught with immensely momentous results.
The history of our blessed, though now calumniated, Reformation, shews the same sovereign control of the royal heart. Henry VIII. was employed as an unintentional instrument, and his godly son as a willing agent, in furthering this great work. The recollection encourages us to refer all anxious care for the Church to her great Head; to rejoice that not kings, but the King of kings reigneth. (Isaiah 9:6.) And shall not we be quickened to earnest prayer for our beloved sovereign (1 Timothy 2:1-3), that her heart, being in the LORD’s hand, as rivers of water, may be disposed to rule for his glory, as a nursing-mother to the Church (Isaiah 49:23), and a blessing to her people?