God is immutable. This is a fancy way for saying God does not change. The immutability of God is found all throughout Scripture and it should give us absolute confidence in the perfect, loving, holy nature of our God. God is unchangeable in His very nature, in His perfections, purposes, promises, and gifts.
Malachi 3:6 says, "I the Lord do not change."
The dictionary definition of immutable is this: "unchanging over time or unable to be changed."
We know from Scripture that God is eternal. There is no beginning nor end for God. As difficult as it is for humans living in the constraints of time to understand, God lives outside the constraints of time. Psalm 33:11 shows us God's existence outside of time constraints: "The counsel of the Lord stands forever, The plans of His heart from generation to generation."
Psalm 41:13 says, "Blessed be the Lord, the God of Israel, From everlasting to everlasting. Amen and Amen."
Jesus said this in His Priestly Prayer found in John 17:5, "Now, Father, glorify Me together with Yourself, with the glory which I had with You before the world was."
We know God is unchangeable because of His omniscience. When a human changes his or her mind, it is because they discovered new information that supersedes old information. God knows everything, therefore He will not change His mind because He knows the absolute truth about all things at all times.
Isaiah 40:28 says, "Have you not known? Have you not heard? The Lord is the everlasting God, the Creator of the ends of the earth. He does not faint or grow weary; his understanding is unsearchable."
Because God does not change, and is perfect, He keeps His promises. His Word stands eternal. We can base our entire world view, beliefs, and perspectives on God's Word.
Numbers 23:19 says, "God is not a man, that He should lie,
Nor a son of man, that He should repent; Has He said, and will He not do it? Or has He spoken, and will He not make it good?"
While God does not change, His interactions and dealings with humans change. We see the way God had outward dealings with people in the Old Testament dispensation that are different from the way He interacted with people during the New Testament dispensation. We can count on the fact that in God's immutability, He will allow His plan to unfold in the order that He has deemed it to unfold. As humans, we see in part, but God, sees the whole. He sees from beginning to end and He knows that both the Old Covenant and the New Covenant point to Jesus Christ as our Savior.
Let yourself relax and trust God more and more as His plan for humankind unfolds. He is immutable and that means His love for us never goes away. He never decides to abandon His plan for the ages. God never changes His nature. Isn't that awesome to ponder?
Hebrews 6:17-18 says, "So when God desired to show more convincingly to the heirs of the promise the unchangeable character of his purpose, he guaranteed it with an oath, so that by two unchangeable things, in which it is impossible for God to lie, we who have fled for refuge might have strong encouragement to hold fast to the hope set before us."