People often take Creatio Ex Nihilo as an argument for the existence of God, however, it can only be a theological statement; that unlike man, God doesn’t create by merely rearranging something which already exists.
The argument Ex Nihilo Nihil Fit is what actually makes the idea of God sound because it is true by experience, definition, and by observation that “nothing” isn’t a possible state of affairs. It means that since “nothing from nothing”, and since there is anything at all, then something must be eternal. This doesn’t mean we can conclude God exists. It only means that we are justified to think of God as eternal if there is a God. The debate on that matter would be over this “Eternal Something” being volitional or non volitional, but that’s not interesting here.
Because one, if not the only, means to suggest God exists is by Ex Nihilo reasoning, we cannot literally claim Creatio Ex Nihilo. If we did, or as soon as we do, we have either claimed nothing can come from nothing or that God is a special exception; and that fallacy shares the same name. God must in some way be said to create of himself, not from nothing at all. Not only that, but given another observation we have by common experience, Sicut A Simili, God must in some way be like that which is created. For example, dogs are not born of cats and even streams of consciousness flow in the same direction no matter the number of forks. “Like effects necessarily follow from like causes” (David Hume, A Treatise On Human Nature; Book 1: Of The Understanding/Part III, Section XV, Rules By Which To Judge Of Causes And Effects). This is a terribly old Aristotelian idea.
All things considered and accounted for, there is an eternality which exists because other things exist, and all contingent things which exist are necessarily some form of that eternality itself.
This means that if you believe this “Eternal Something” is volitional, then all that is implied is that there is a mindful reason why anything else exists. You likely call this eternality, “God”. Given that God is defined as immaterial and given Sicut A Simili, materiality is an accidental property of existence. How God must be like creation, causal to it without being material himself, is in the idea that God is the “Ground Of All Being” and not a specific instance of something which exists; which is to say in the regular sense, “something which manifests” in material form.
While the entire matter of volition is completely debatable, what isn’t is what follows from the idea of volition given. That is, God has a reason in creating anything at all. And in all cases, what has been created is like its cause. Quite literally then, all that exists is from God and is an expression of God and is in some way God.
Creatio Ex Se; God created from himself.