Weinandy on Divine Immutability

One should not be misled into thinking that God’s immutability is like the immutability of a rock only more so. What God and rocks appear to have in common is only the fact that they do not change. The reason for their unchangeableness is for polar-opposite reasons. The Rock of Gibraltar does not change or changes very little because it is hardly in act at all, and the change that it does undergo is mainly from outside causes—wind and rain. God is unchangeable not because he is inert or static like a rock, but for just the opposite reason. He is so dynamic, so active that no change can make him more active. He is act pure and simple . . .

What the critics consistently fail to grasp is that God’s immutability is not opposed to his vitality. Nor need one hold together in some dialectical fashion his immutability and his vibrancy, as if in spite of being immutable he is nonetheless dynamic. Rather, it is precisely God’s immutability as actus purus that guarantees and authenticates his pure vitality and absolute dynamism. Thus, when the critics assert that because Aquinas and the tradition believe God to be immutable they espouse a static and inert conception of God, they but demonstrate their own lack of understanding.

(Thomas Weinandy, Does God Suffer? 78–79, 124)