John Calvin writes in the institutes:

when he says, “The king’s heart is in the hand of the Lord as the rivers of water; he turneth it whithersoever he will,” (Prov. 21:1), he comprehends the whole race under one particular class. If any will is free from subjection, it must be that of one possessed of regal power, and in a manner exercising dominion over other wills. But if it is under the hand of God, ours surely cannot be exempt from it.

Right doctrine…

It is perfectly legitimate to say that what is true of kings is true of everyone. If one believes that king’s are as accountable for their actions as anyone else, then Proverbs 21.1 gives us warrant for applying what is said about kings to everyone else.

…but not THE point of the text.

That said, the point of Proverbs 21.1 is not to teach God’s absolute control over human decisions. If it was, then the verse would say that “A man’s heart is in the hand of the Lord as the rivers of water…” And that is not what God chose to say. Why did God single out the king?

The context

While I am not going to claim to have a great grasp of the structure of Proverbs, it isn’t hard to notice that in the neighboring chapters Solomon gives the reader advice on how to behave before kings and comments one how to get their attention.

Watch the King especially

If my (rather unstudied) observation is correct, then the point of Proverbs 21.1 is not simply to assert the doctrine that God is in control, including everyone’s decisions, but to make the specific point that God works through rulers. Paul, even in a pagan context, expected God to eventually reward godly behavior and invited Christians to ask themselves why they weren’t being so rewarded (Romans 13.1-7).

God’s plan for the Gospel

Proverbs 21.1 may ultimately be important for redemptive history–to say that God himself was behind the condemnation of Jesus (Acts 4.24-28). Herod and Pilate did what God wanted them to do, at one level.

Abstraction & premature abstraction

Calvin abstracts a truth from Proverbs 21.1 that is undoubtedly true. There is no problem in teaching the doctrine he wants to teach from the passage. The problem would arise in “leaving” the passage “behind” as if it was already understood at this point. While Calvin’s teaching is justified on the basis of Proverbs 21.1, he has not correctly stated the meaning of the verse. We know this because a particular word God chose to use (“king”) gets lost if we stop with Calvin’s use as the main intention of the passage. It is good and necessary to abstract principles from texts but it is not good to stop our passage with details left untouched.

There may be a time to only deal with our own issues (i.e. defending the truth from those who would deny God’s control of history). But our calling is to listen to God’s issues as revealed in the particulars of God’s Word.

Conclusion: Biblical Theology & Systematic Theology

This exemplifies, I think, the difference between Biblical theology and systematic theology. ST tends to emphasize abstracting the statements to gain a philosophical understanding about the world. BT tends to focus on the story of the Bible. Both are necessary but often ST can often produce an illusion of comprehensiveness when it actually doesn’t find parts of the Bible useful. BT is a good and necessary corrective to this temptation.