Immutable means unable to be changed. So, when something is immutable it can never be anything other than what it is.
God does not change.
Does that mean that God is a statue forever fixed in a pose? No. God’s immutability is in His character.
His will does not change. His promises do not change. His plans do not change. His character does not change. Also, God cannot become more or less wise, more or less just, more or less merciful, or more or less powerful. He is who He is, and that is who He will always be.
What God has planned, He will complete. What God has promised, He will fulfill. What God desires, He will always desire. What pleases God will always please God, and the same goes for what displeases Him.
God’s immutability is a great comfort to us because it means that we can trust and rely on Him. We can trust that He will fulfill His promises. We can rely on Him to do what He says He will do. And we can always know what He generally wants us to do.
He doesn’t promise something and then “forget.” He doesn’t say He will do something and then not actually be able to do it. He doesn’t have a different personalized “truth” for each individual. And He doesn’t suddenly change His mind so that what was once a good thing suddenly becomes a bad thing.
And God is to be praised for His immutability. Can you imagine serving an uncertain, or incomplete, or “evolving” God? It would be worse than trying to keep up with the latest fad diet. One day you can’t eat fat, the next you can eat fat, but not sugar, then you can only eat meat, and then only vegetables, and then you can eat everything but in limited quantities… It would be an eternity of torture to have to constantly try to keep up with a God that is not unchanging.
Also, since God does not change, that means we can really know Him. I’m not saying we will ever be able to fit all of God into our minds. What I’m saying is that once you learn something about God, you can trust that the thing you know about God will never change. God does not have to figure out “who He is,” so we don’t have to worry about Him changing aspects of His identity. He’s not a meat eater one week, and then a vegetarian the next, and then gluten-free the week after that, and then something else after that… Everything that you know about God, and I mean really intimately know about Him - not just book knowledge, will always be Him.
This doesn’t mean you won’t find things that appear to be contradictions. How can God be loving and merciful, and yet still judge and punish? God is both. And God has a balance so that His justice doesn’t squash His mercy, and His mercy doesn’t dilute His justice. As a parent we both love and nurture our children, and also correct and punish them. The correction and punishment are done because we love them. And even though we love them more than anything, that doesn’t mean that we never get angry or frustrated with them.
God is like that too. He is not a statue. He is our living Father, and His character never changes even though His current mood toward us might. To that point, as a parent, when my kid makes me mad, I’m generally mad in a way that is apparent to everyone around. But God isn’t like that. God may be extremely mad at one person and extremely happy with another at the same time! He’s God like that…
Finally, we may find ourselves asking God “why” a lot sometimes. But His answer is always the same. It is done according to His will.
We tend to look at things that are going on in our lives, our communities, and the world as somehow being unique to us and our times. But the Bible says that there is nothing new under the sun. And there is nothing new under the sun because everything is working the way God designed it to work - and He has not changed that. And everything is going according to His plan - and He has not changed that. And everything is happening that He said would happen - and He has not changed that.
We cry out to God, “Why, God? Why me, Lord?” and His answer is, and always will be, the same, “Trust me.” And we can trust Him, because He never changes. He is and always will be absolutely reliable, absolutely trustworthy, and absolutely knowable. He will always be God.
Malachi 3:6 (NLT) “I am the LORD, and I do not change. That is why you descendants of Jacob are not already destroyed.
James 1:17 (NLT) Whatever is good and perfect comes down to us from God our Father, who created all the lights in the heavens. He never changes or casts a shifting shadow.
Ecclesiastes 1:9 (NASB95) That which has been is that which will be, And that which has been done is that which will be done. So there is nothing new under the sun.