The king’s heart is like channels of water in the hand of the LORD; He turns it wherever He wishes. Every man’s way is right in his own eyes, but the LORD weighs the hearts. To do righteousness and justice is desired by the LORD more than sacrifice.
John Calvin comments: “Does God work in the hearts of men, directing their plans and moving their wills this way and that, so that they do nothing but what He has ordained?” (Concerning the Eternal Predestination of God, p.174, emphasis mine)
Calvin adds: “The question is whether He has in His power also the depraved affections of the ungodly, moving them here and there so that they will what He has decreed they should do. Certainly when Solomon declares (Prov 21:1) that the heart of kings are in the hand of God so that He inclines it as He pleases, he shows that in general the will not less than external works are governed by the determination of God.” (Concerning the Eternal Predestination of God, p.174, emphasis mine)
Would that mean that God is moving and directing what was already fixed and decreed? The Calvinist argument is self-defeating, when considering that God “weighs the motives” (Proverbs 16:2) “weighs the hearts” (Proverbs 21:2) in “searching all the innermost parts of his being.” (Proverbs 20:27) What exactly would God be weighing and searching if He had decreed what He weighs and searches? These matters only make sense if man has a free-will that God is exploring, and just as reasonably, testing.
Leighton Flowers comments: “It is non-sensical to suggest God is restraining a will that He has already been meticulously controlling.” (Compatibilism’s Quandary)
Arminians, Walls and Dongell, comment: “Indeed, ‘the king’s heart is in the hand of the LORD; he directs it like a watercourse wherever he pleases’ (Proverbs 21:1). But it is unwarranted to transform this verse into the claim that God has actually chosen to control not only every decision of the king but also every decision made by every human being ever born. It is also unwarranted to extend focus of this verse from its assurance of God’s people that their leader is shaped by divine will, to a claim that the rise of saving faith in any individual heart has been unconditionally caused by God. Furthermore, this verse and others like it (e.g., Ps 135:6) can be parlayed into total determinism only by presuming that God’s will itself contains divine preferences for the movement of every molecule, for every electrical impulse, for every rustling leaf, for every human thought. Conclusions of these sorts can be reached only by importing convictions and beliefs into these texts.” (Why I am not a Calvinist, p.63)
One member of The Society of Evangelical Arminians explains: “I don’t think verse 1 should be understood apart from verses 2 and 3. The king’s heart is like a stream of water when it is in the hand of the Lord, when the king submits himself to God for wisdom and guidance, for proper direction. That makes the text of 21:1 complementary to the following two verses. Calvinists, on the other hand, suggest that God directs the hearts of kings in all they do. But that would mean that God himself directed Solomon (as well as the other kings) to embrace idolatry, which is something that God directly repudiates in the Law. That would mean that God essentially commits the sin of Balaam for him.” (SEA)