From Bruce Ware’s Their God is Too Small: Open Theism and the Undermining of Confidence in God:
He is God, not man, and as God, he is above any “regret” in this strong sense (v. 29). But second, just because God does not ever question what is happening (since he knew it all previously), we should not conclude that he doesn’t care about the sin that unfolds. He does! He is deeply dismayed at what Saul does as he witnesses the unfolding of what he previously knew would occur. And as God observes Saul’s sin, he bemoans the disobedience and harm that Saul’s actions reflect. So, he “regrets” (in a weak sense) Saul’s king-ship, even though he knew and planned all along what is actually transpiring.
The first thing to notice about this quote is that Ware rewrites the narrative of 1 Samuel 15. Just by reading the story, a casual reader will not walk away with the understanding that Ware presents.
In the first few verses of 1 Samuel 15, God commands Saul to kill the Amalekites. Saul does so but spares the livestock and the king. God then says He regrets making Saul king. If the author had any notion that this rebellion was “foreknown” this would be the time to mention something, anything. But the author has God responding to events as they unfold. God regrets and regrets without apology or qualification.
Samuel then confronts Saul as says because Saul has rejected God that God rejects Saul. Samuel also says that day God has torn the kingdom from Saul. Saul reigns another 18 years after this, so it should be obvious that God decides to tear the kingdom from Saul once He sees Saul rebel in this chapter. Over this, Samuel says that God is not a man that He should repent. The narrative then says that God repents of making Saul king.
Ware plays coy when he does not address the very obvious fact that Samuel’s words are limited to the context of God giving Saul back the kingdom. Both God and the narrator are clear that God has repented, and God seeks out David as evidence of this repentance. The repentance is crucial to the narrative, whereas Ware’s understanding of immutability invalidates the narrative. Ware discounts both the narrator and God’s own words in favor of an idiosyncratic understanding of Samuel’s words.