6 “For I the LORD do not change; therefore you, O children of Jacob, are not consumed. 7 From the days of your fathers you have turned aside from my statutes and have not kept them. Return to me, and I will return to you, says the LORD of hosts. But you say, ‘How shall we return?’ 8 Will man rob God? Yet you are robbing me. But you say, ‘How have we robbed you?’ In your tithes and contributions. 9 You are cursed with a curse, for you are robbing me, the whole nation of you. 10 Bring the full tithe into the storehouse, that there may be food in my house. And thereby put me to the test, says the LORD of hosts, if I will not open the windows of heaven for you and pour down for you a blessing until there is no more need. 11 I will rebuke the devourer for you, so that it will not destroy the fruits of your soil, and your vine in the field shall not fail to bear, says the LORD of hosts. 12 Then all nations will call you blessed, for you will be a land of delight, says the LORD of hosts“For I the Lord do not change” is the basis of this entire passage and introduces some attributes of God.
“For I the Lord do not change”—God is a self-existent, eternal being in whom there is no shadow of change.
First, God is independent. Wayne Grudem offers a good definition.
God’s independence is defined as follows: God does not need us or the rest of creation for anything, yet we and the rest of creation can glorify him and bring him joy. This attribute of God is sometimes called his self-existence or his aseity (from the Latin words a se which mean “from himself “).
Lutheran theologian J.T. Mueller adds,
This means simply that God depends on no one for anything, that God is self-sufficient in His being and in His purposes. His divine aseity (aseitas), according to which God is absolutely of Himself and independent of anything outside Himself, Rom. 11: 36. ( 36 For from him and through him and to him are all things. To him be glory forever. Amen.)W.G.T Shedd points out that, “(w)hen applied to God, aseity means that he has his existence in and through himself (a se), rather than being dependent in any way on another for his existence.”
Beyond His aseity, God exists eternally. He is eternal.
Grudem again offers our definition. “God’s eternity may be defined as follows: God has no beginning, end, or succession of moments in his own being, and he sees all time equally vividly, yet God sees events in time and acts in time.”
In Psalm 90:2 the Psalmist tells us that, “Before the mountains were brought forth, or ever you had formed the earth and the world, from everlasting to everlasting you are God.”
Edward Busch relays the teaching of Barth on this issue.
"Only God is eternal,"...The eternity of God means that he is "free to be constant," and the reason for this is that "time has no power over Him.... As the One who endures He has all power over time" (II/1 687 = 609). As the Eternal One, He "is not conditioned by time, but conditions it absolutely in His freedom" (11/1 698 = 619). He does not owe his existence to time, but all temporal being owes its existence to him.Bruce Ware, in his great work on relaying deep theological truths to young minds, explains God’s aseity and eternity clearly.
God is eternal. This means that God’s life has no beginning, and it has no ending. Unlike everything else that has ever existed, God does not depend on anything else for his life, since he always lives and can never die. This is a very difficult idea for us to understand, since we do not know of anything like this—and that’s because there is nothing in all of creation that is like God. Your own life had a beginning, when you were first conceived, and then nine months later you were born into this world. And your mom and dad both began at some time, as has every dog, cat, lion, elephant, tree, and insect. Everything else has a beginning to its life. But this is not true of God. God has no beginning, since he always lives. And because life is part of what it means for God to be God, his life can never come to an end…When Moses speaks of God as living “from everlasting to everlasting,” he means that as far back as you can think (even before God created the universe and created time itself) to as far forward as you can think (imagine heaven that continues millions and billions of years from now), God has always lived and will always live. From the everlasting past to the everlasting future, God has always existed as God and always will. So, the true and living God has life in himself. No one has given him life, and no one can take away that life. Because God is God, he always lives.
Because God has life in himself, this also means that God has every-thing that he needs for his life in himself. After all, since God lives forever, it must be true that God has lived most of his life when there was nothing else. God lived before he created the world, and he was still fully God then. So, for God to have life in himself, it means that he also must have everything that he needs for his own life within himself. We can think of God, then, as being both self-existent (he has life in himself) and self-sufficient (he has everything he needs for his life in himself). This reminds us…that God has no need for the world, since everything God needs to be God is found in his own life. Because God is eternal, because he has life in himself, it also means that he has every good thing within his own life. Nothing can be added to the richness that God has because God has it all, without beginning and without ending.