Seen from a logical viewpoint, there are several reasons why it is impossible for God to change. First, if anything changes it must do so in some chronological order. There must be a point in time before the change and a point in time after the change. Therefore, for change to take place it must happen within the constraints of time; however, God is eternal and exists outside of the constraints of time (Psalm 33:11; Psalm 41:13; Psalm 90:2-4; John 17:5; 2 Timothy 1:9).
Second, if anything changes it must change for the better or the worse, because a change that makes no difference is not a change. For change to take place, either something that is needed is added, which is a change for the better, or something that is needed is lost, which is a change for the worse. But since God is perfect, He does not need anything. Therefore, He cannot change for the better. If God were to lose something He would not be perfect; therefore, He cannot change for the worse.
Third, when someone changes his/her mind, it is often because new information has come to light that was not previously known, or the circumstances have changed that require a different kind of attitude or action. Because God is omniscient, He cannot learn something new that He did not already know. So, when the Bible speaks of God changing His mind, it must be understood that the circumstance or situation has changed, not God. So when Exodus 32:14 and 1 Samuel 15:11-29 talk about God changing His mind, it is simply describing a change of dispensation, and outward dealings, toward man.
Numbers 23:19 is very clear, “God is not a man, that He should lie, nor a son of man, that He should change His mind. Does He speak and then not act? Does He promise and not fulfill?” No, God does not change His mind. These verses affirm the doctrine of God’s immutability: He is unchanging and unchangeable.