The doctrine of creatio ex nihilo says that God causes things to exist as numerically distinct from Him — i.e., as having an existence of their own, separate from His — without acting upon something preexistent. What I will call qualified monism (or panentheism) is the view that God causes things to exist as distinct from Him by bringing them about as modifications of His own being. An analogy I like to use for this is as follows. Just as one might bring about a fist by flexing the muscles in one’s hand and arm, so also God “flexes” His power and brings about that something comes to share in His existence. Creatio ex nihilo thus asserts that there is both a distinction and a distance between God and things, whereas qualified monism asserts that there is a distinction without a distance between God and things.
Both of these views can agree on quite a lot. For example, proponents of either view can agree that God must exist of Himself and be the source of the existence of everything else. Proponents of either view can also agree that there is a difference between God and everything else, so that He is not straightforwardly to be identified with all the various things that He causes to exist. The only difference has to do with the matter of distance. Creatio ex nihilo says there is an ontological distance between God and creature akin to the ontological distance between myself and another person. Qualified monism says that there is ontological difference without distance as in the case of myself and the fist I form.
Is there any reason to prefer one view to the other? I think so. Here is an argument. There are various ways we justify distinguishing between things. One way is by finding a difference in qualities. This pen is red whereas that piece of paper is white; I can pick one up while the other remains unmoved; I can destroy the pen while the paper remains; and so on. In this way, the pen and the paper show themselves as distinct and independent experiential unities. This is how I come to the conclusion that they are distinct things. But there is nevertheless one quality both of these things have in common all the time: namely, that of being apparent, of “showing up.” Indeed, the pen and the paper alike can be appreciated as distinct “regions” of a single appearing “mass“ that is the world of experience. But then there is no strict ontological distance between the pen and paper any longer at this level. There is just a single appearing “thing” that “takes the shape” of a pen or of a paper in different places.
There is thus a point of view from which the differentiation of things is most obvious. This is the point of view we are almost always in, all day long. We take it for granted. We always take ourselves to be dealing with a diversity of things presented to us as distinct from each other. But it is also possible to consider things from a slightly different angle and thus to perceive a certain fundamental unity underneath the more familiar level of diversity and differentiation. One could say that this fundamental unity is God. This apparent “mass” that is constantly showing itself in a diversity of modes and modifications is precisely God Himself making Himself known to people. All the diverse objects we are used to seeing and differentiating from each other are modifications that God brings about in His own being just like we can bring about a fist by flexing the muscles in our hands and arms. Experience thus supports the qualified monist position.
The reply from the side of the proponent of creatio ex nihilo is that this thought-experiment is entirely wrong. God is pure being and thus cannot be experienced. He lies outside the world of experience altogether and can only be thought about and contemplated by the intellect. But this conception of things assumes that appearance and being are distinct and uncorrelated. What appears may not be and what is may not appear. I deny this and have argued on phenomenological grounds that this point of view leads to skepticism. See this video here. Thus, I do not allow a distinction between the sphere of appearance and the sphere of being. They are one and the same sphere. And if God is to exist, He must show up in the sphere of appearance. The qualified monist position shows how this can be.