Classical Christian theism is deeply devoted to the absoluteness of God with respect to His existence, essence, and activity. Nothing about God's being is derived or caused to be. There is nothing beyond Him or outside Him that could increase, alter, or augment His infinite fullness of being and felicity. For this reason, He cannot subject Himself to changes because every change involves a cause that brings the subject an actuality of being that the subject lacks in and or itself. [James E. Dolezal, All That is in God: Evangelical Theology and the Challenge of Classical Christian Theism (Grand Rapids, MI: Reformation Heritage Books, 2017), 10]
14. God cannot give being to Himself since He cannot give what He does not have; and if already possess the fullness of being, He cannot receive it from Himself. No one is enriched in any way by what one already possesses. Such a notion of giving and receiving that of which one is already in perfect possession is trivial at best and nonsensical at worst. Enrichment requires addition of actuality. God can have nothing added to Him because He lacks no perfection of being and actuality. (Dolezal, 17 footnote 14)
[Before we start, let me just state that I hold to divine perfection, and the aseity, infinity, immutability, impassibility, and simplicity of God. That done? Let's begin.]
God is God. He is infinite, and His existence and essence is most certainly absolute. He is fully a se, and thus dependent on no one for anything. That all is true. However, it is truly fascinating how that can be used to translate into an argument for immutability. Worse still is how natural theology is retrofitted as something appropriate for the 21st century. It is shocking and disturbing how natural theology is making a comeback, as if Scripture alone is insufficient and nature sufficient to inform us about who and what God is in His fullness. It is almost as if we did not learn anything from Vatican I and the Thomisms that spawned from it, thinking that somehow a revival of Thomas Aquinas is beneficial to the Protestant church!
In God's providence, the conclusions about who God is as delivered through classical theism have been true to the Scriptures. But just as God can use crooked sticks to draw straight lines, so likewise just because God had used Aristotelian and Thomistic metaphysics does not imply that the tools used are somehow sacrosanct. There comes a time when, upon further reflection, we might see the limitations of these tools and how using them further would harm us and our knowledge of God. It is my opinion that such a time has come, as the attempt to revive Thomistic metaphysics in the modern day has resulted in more problems than it actually solves.
In Dolezal's book, the basic premise of the Ontological argument is rephrased and refitted into an argument for immutability. Since God has perfect infinite being, therefore there cannot be any changes in God. Utilizing Thomistic categories, God's infinite perfection must imply full actuality (purus actus) and immutability. The reason why infinite perfection implies immutability is because change implies potentiality, and any change is a change away from perfection, which shows that God is not infinitely perfect. But since God is infinitely perfect, therefore God must be immutable and is pure act.
From a natural theology perspective, we cannot smuggle in propositions from Scripture. So therefore, arguing from philosophy alone, why must we accept the argument that infinite perfection must imply that any change would be against God's infinite perfect nature? Dolezal argues that "there is nothing beyond Him or outside Him that could increase, alter, or augment His infinite fullness of being and felicity." Very true, only if we hold to aseity. But what about changes within God Himself? Here, Dolezal claims that "every change involves a cause that brings the subject an actuality of being that the subject lacks in and or itself." But this is not necessarily the case. "Perfection" apart from its biblical content can mean a lot of things, and it is not evident that "perfection" must imply the existence of some form of infinite good that is by definition unsurpassable by anything else. Likewise with the word "infinite." A black holes is an infinite singularity "cordoned off" from the rest of the universe by its event horizon, yet it has finite mass and occupies finite (3D) space. So what does "infinite" really mean?
Is there even such a conception as a "perfect being" rightly understood according to Platonism? In evolutionary biology, "perfection" does not exist, for an organism perfectly suited for its ecosystem can suddenly be ill-fitted when the world and its habitats change. So what is "perfection"? Static immutability is far from perfect in biology! So what exactly do we mean by "infinite" and "perfection" since we are defining it according to natural theology (which cannot be limited to only Thomistic natural theology, but is to refer to all attempts to think about God from a earthly perspective!)
Since such is the case, Dolezal's statement that "[God] cannot subject Himself to changes because every change involves a cause that brings the subject an actuality of being that the subject lacks in and or itself" is false according to the full version of natural theology. It is first false because "infinite perfection" can be defined as supreme adaptability to all forms of changes, as in biology. It is second false because all changes can be to the accidents and not the substance of being, as when wolves adapt to become various species of dogs yet they still are part of the wolf kind. [It may be objected that that is a denial of simplicity, but that is not part of Dolezal's argument, which claims that infinite perfection ALONE implies immutability and pure act.] Thirdly, it is false because change from within can come about through internal processes yet without affecting the ontology of the being itself, as when mental discipline can allow for humans to do some remarkable things like walking on fire and on needles, yet nothing is changed in the essence of the the person himself.
But, if Thomstic metaphysics can get us to what the Bible explicitly teaches (God as perfect, God as infinite, God as immutable), why should we be hung up over the manner we get to those? It matters because method is not neutral, and the method has the potential to lead us to an undermining of what the Bible teaches in other places. After all, the Bible does not teach Aristotle neither is the Summa Theologia the 67th book of the Bible. If we truly practice Sola Scriptura, then even concerning the doctrine of God which has been served rather well by classical metaphysics, we must hold the method critically at arm's length. From my perspective, I do not see any necessity of utilizing classical metaphysics besides historical theology, as I am confident that the Bible alone is sufficient to provide us the whole doctrine of God, utilizing classical metaphysics as the skeletal form to direct our theologizing, and nothing else.