The Immutability of God
Immutability is one of the Divine perfections which is not sufficiently pondered. It is one of the excellencies of the Creator which distinguishes Him from all His creatures. God is perpetually the same; subject to no change in His being, attributes, or determinations. Therefore God is compared to a rock (Deut. 32:4, etc.) which remains immovable, when the entire ocean surrounding it is continually in a fluctuating state; even so, thought all creatures are subject to change, God is immutable. Because God has no beginning and no ending, He can know no change. He is everlasting “the Father of lights, with whom is no variableness, neither shadow of turning” (James 1:17).
First, God is immutable in His essence. His nature and being are infinite, and so subject to no mutations. There never was a time when He was not; there never will come a time when He shall cease to be. God has neither evolved, grown, nor improved. All that He is today, He has ever been, and ever will be. “I am the Lord, I change not” (Mal. 3:6) is His own unqualified affirmation. He cannot change for the better, for He is already perfect; and being perfect, He cannot change for the worse.
Second, God is immutable in His attributes. Whatever the attributes of God were before the universe was called into existence, they are precisely the same now, and will remain so forever. Semper idem (always the same) is written across every one of them. His power is unabated, His wisdom undiminished, His holiness unsullied. The attributes of God can no more change than Deity can cease to be. His veracity is immutable, for His Word is “forever settled in heaven” (Psalm 119:89).
(Pink, The Attributes of God, 37-38)