By John MacArthur in his foreword to Foundations of Grace: A Long Line of Godly Men by Steve Lawson.
The Bible repeatedly and unapologetically underscores the fact that God does not change. In fact, He cannot change because He cannot improve on absolute perfection or decline in His eternally fixed nature. His person does not change: “For I the LORD do not change” (Mal. 3:6). His plans do not change: “The counsel of the LORD stands forever, the plans of his heart to all generations” (Ps. 33:11). His purpose does not change: “So when God desired to show more convincingly…the unchangeable character of his purpose, he guaranteed it with an oath” (Heb. 6:17). God does not change His mind: “The Glory of Israel will not lie or have regret, for he is not a man that he should have regret” (1 Sam. 15:29); or His words: “The Holy One of Israel…does not call back his words” (Isa. 31:1-2); or His calling: “The gifts and the calling of God are irrevocable” (Rom. 11:29; cf. Heb. 13:8; James 1:17). There are absolutely no changes in God, no variations, and no surprises (cf. Ps. 102:27).
God does not increase or decrease. He does not improve or decline. He does not change due to some altered circumstances – there are no unforeseen emergencies to the One who is eterally all-knowing. His eternal purposes stand forever because He stands forever (Ps. 33:11). He does not reacts, He only acts – and He does so however He pleases (Ps. 115:3).
From a human perspective, of course, God sometimes appears to change His plans or His actions based on what people do. But this is not so from God’s viewpoint. Because He knows and always has known the future perfectly, having planned it according to His unalterable decree. He always acts in the way that He planned to act from eternity past. While men do not know how God will act, and are sometimes astonished as they see His sovereign plans unfold, God is never surprised. He continues to work as He always has, according to His eternal purpose and good pleasure (cf. Ps. 33:10-12; Isa. 48:14; Dan. 4:35, Col 1:19-20)