Malachi 3:6 (ESV) … “For I the Lord do not change; therefore you, O children of Jacob, are not consumed.”
The Lord assures his people that he has not changed (v. 6). Change can only go in one of two directions, that is, becoming better or worse. The Lord can do neither. He cannot become better because he is already perfect, and he cannot become worse because he can in no way deteriorate or become less than he already is.
The Lord also points out that the people of Israel had not changed (v. 7). They were disobeying him as their forefathers had done, but the unchanging nature of the Lord would not allow him to destroy them. He had committed himself to Israel, and he must keep his promise. His unchanging nature also guaranteed that he would return to them if they would return to him. Once again, it was a matter of God being faithful to his promises.
We are dealing with the same unchanging God who requires obedience and who forgives those who repent of disobedience (1 John 1:9). In a world of flux and change, he is the constant.