The Immutability of God is a necessary concomitant of His aseity. It is that perfection of God by which He is devoid of all change, not only in His Being, but also in His perfections, and in His purposes and promises. In virtue of this attribute He is exalted above all becoming, and is free from all accession or diminution and from all growth or decay in His Being or perfections. His knowledge and plans, His moral principles and volitions remain forever the same. Even reason teaches us that no change is possible in God, since a change is either for better or for worse. But in God, as the absolute Perfection, improvement and deterioration are both equally impossible. This immutability of God is clearly taught in such passages of Scripture as Ex. 3: 14; Ps. 102: 26-28; Isa. 41: 4; 48: 12; Mal. 3: 6; Rom. 1: 23; Heb. 1: 11,12; Jas. 1: 17.
Berkhof, Louis. Systematic Theology (p. 46). . Kindle Edition.