God himself does not change. He is as he always has been and will always be. But many Christians who would affirm that statement believe, on the basis of circumstances and experience, and even on the basis of a few passages of Scripture, that God does change his mind. How shall we answer them? J. I. Packer writes, “God’s purposes do not change.”
“He who is the glory of Israel does not lie or change his mind,” declared Samuel, “for he is not a man who should change his mind” (1 Samuel 15:29). . . .
Repenting means revising one’s judgment and changing one’s plan of action. God never does this; he never needs to, for his plans are made on the basis of a complete knowledge and control which extend to all things past, present, and future, so that there can be no sudden emergencies or unexpected developments to take him by surprise. “One of two things causes a man to change his mind and reverse his plans: want of foresight to anticipate everything, or lack of foresight to execute them. But as God is both omniscient and omnipotent there is never any need to reverse his decrees” (A. W. Pink). “The plans of the Lord stand firm forever, the purposes of his heart through all generations” (Ps 33:11).
What God does in time, he planned from eternity. And all that he planned in eternity he carries out in time. And all that he has in his Word committed himself to do will infallibly be done. . . . No part of his eternal plan changes.
It is true that there is a group of texts (Gen 6:6–7; 1 Sam 5:11; 2 Sam 24:16; Jon 3:10; Joel 2:13–14) which speak of God as repenting. The reference in each case is to a reversal of God’s previous treatment of particular people, consequent to their reaction to that treatment. But there is no suggestion that this reaction was not foreseen, or that it took God by surprise and was not provided for in his eternal plan. No change in his eternal purpose is implied when he begins to deal with a person in a new way.
–J. I. Packer, Knowing God |Thirsty Theologian