What is the significance of 1 Samuel 15:35?

“…the Lord was sorry that he made Saul king over Israel.” (see 1 Sam. 15:12).

Once again, the Lord expresses his regret over having made Saul king of Israel, an emotion which is inconsistent with the classical view of God’s foreknowledge.

It’s important to note that Samuel had prayed all night trying to change the Lord’s mind regarding Saul’s dethronement (vs. 13) but in this instance it seems the Lord’s decision was final (cf. 1 Sam. 13:13–14). Hence, as Saul begged Samuel to try to change things (vs. 27), Samuel responded, “the Glory of Israel will not recant or change his mind for he is not a mortal, that he should change his mind” (vs. 29).

The verse does not say that God cannot change his mind (which is what the classical view requires), only that in this instance he will not change his mind. His mind is resolved on this matter and, unlike mortals, once God’s mind is truly resolved he does not change it. (There are other verses in which the Lord declares “I will not change my mind” [Ezek. 24:14; Zech. 8:14], but these exceptions prove the rule: ordinarily God is willing to change his mind if the situation calls for it [cf. Jer. 18:7–10; Jon. 4:2; Joel 2:12–13]).