For I am the LORD, I change not; therefore ye sons of Jacob are not consumed.
To announce that you’re going to speak on the immutability of God is almost like putting up a sign saying, “There’ll be no service here tonight!” Nobody wants to hear anybody talk about it, I suppose. But when it’s explained, you’ll find you’ve struck gold and diamonds, milk and honey.
Now the word immutable, of course, is the negative of mutable. And mutable is from the Latin, meaning “subject to change.” Mutation is a word we often use to mean “a change in form, nature or substance.” Immutability, then, means “not subject to change.”…
Now there is in God no mutation possible. As it says in James, “with whom is no variableness, neither shadow of turning” (1:17)—there is no variation due to change. And there is also that verse in Malachi: “I am the LORD [Jehovah], I change not” (3:6)….
Incidently, He’s the only One in the universe that can say that. And He did say it! He simply says that He never changes, that there is no change possible in God. God never differs from Himself. If you get ahold of this, it can be to you an anchor in the storm, a hiding place in danger. There is no possibility of changing in God. And God never differs from Himself. AOGII089-091
Thank You, Father, that despite my ever-changing world You are ever constant, my anchor in the storm. Amen. 
3:6 The fact that the Lord is the unchanging One accounts for the preservation of the sons of Jacob from destruction.
6 The second issue of communal disobedience raised by Malachi lies in the area of stewardship. God has blessed them, but they have failed to reciprocate by returning to him what the law requires. The Lord rebukes them with more than a little hint of impatience, but it is impatience generously leavened by grace (v. 6). Without that grace he would long since have destroyed them for their lack of compliance.
3:6 I the Lord do not change implies that God’s character and eternal purposes do not change, which gives a solid foundation for his people’s faith and hope. However, unchangeableness in character does not mean that the Lord is unchanging in his actions, for the very next verse, “Return to me and I will return to you” (v. 7), shows that God acts differently in response to different situations. Therefore implies that God’s purpose to bring blessing to the world through Abraham’s descendants and through a Davidic Messiah will not be defeated, and thus the children of Jacob are not consumed: their existence as the restored community is evidence of God’s faithfulness.
3:6 I, Yahweh, have not changed The primary reason Israel has not been destroyed is because of Yahweh’s faithfulness to His covenants with the nation. Yahweh will not change His mind concerning Israel.
3:6 I … do not change. The immutability, or unchangeable character, of God is seen in His purpose to bless His elect people. Thus, in spite of their numerous sins, they are not destroyed (Ex. 34:6, 7; Jer. 30:11). This verse closes the previous section and begins the next one.
 Tozer, A. W., & Eggert, R. (2015). Tozer on the almighty god: a 365-day devotional. Chicago, IL: Moody Publishers.
 MacDonald, W. (1995). Believer’s Bible Commentary: Old and New Testaments. (A. Farstad, Ed.) (p. 1176). Nashville: Thomas Nelson.
 Merrill, E. H. (2008). Malachi. In T. Longman III & D. E. Garland (Eds.), The Expositor’s Bible Commentary: Daniel–Malachi (Revised Edition) (Vol. 8, p. 858). Grand Rapids, MI: Zondervan.
 Crossway Bibles. (2008). The ESV Study Bible (p. 1778). Wheaton, IL: Crossway Bibles.
 Barry, J. D., Mangum, D., Brown, D. R., Heiser, M. S., Custis, M., Ritzema, E., … Bomar, D. (2012, 2016). Faithlife Study Bible (Mal 3:6). Bellingham, WA: Lexham Press.
 Sproul, R. C. (Ed.). (2015). The Reformation Study Bible: English Standard Version (2015 Edition) (p. 1654). Orlando, FL: Reformation Trust.