The church father Tertullian (200 AD) was rightly a staunch materialist who realized that all of the biblical data - not just some of it, literally all of it - favors a wholly physical God.
Tertullian is one of the greats, but certainly only one. His materialistic approach to God's nature is on the fringe compared to the greater majority of Christian thinkers before him and after him. If you are a Tertullianite, fine. But that also means you are on the fringe. That should give you some pause when considering the level of credence you give to your own position. That's not to say you're wrong. Maybe you and Tertullian are correct and the vast majority of Christians who have considered related questions are wrong. But, your confidence level should be tempered. Even Tertullian did not reject all of Plato (e.g. that the soul is simple and not compound). And it's that very aspect that puts your understanding of "physical" and "material" into question. It doesn't seem you have thought through what it means for something to be physical.
There is no burden of proof on materialists because the existence of material object is not an extraordinary claim. Matter is something we see every day. Whereas immaterialism
Several church fathers acknowledged that angels are physical - and yet God (normally) keeps them hidden from material instruments.
First we have the translocation of the Son - and it's a wholly physical event...
You're not being consistent here. On the one hand, your argument rests on the notion that matter and the physical are part of our everyday experience, and so there is no burden of proof on the part of the materialist who asserts that God is corporeal. On the other hand, your examples of angels and the post-resurrected Christ are instances that don't fit our experience of "matter" and "physical" reality. Angelic appearances, no matter how rarefied their supposed physical being, are not part of our everyday experience. If they are physical, in the same space as us, and yet hidden from our sight as substantiated entities, then "matter" and "physical" are taking on characteristics unlike what we know as "physical" and "matter."
Likewise, instances where people simply appear in the room, as Jesus did post-resurrection, are not what one would expect from the physical. I suppose examples where these so-called "physical" beings act in ways wholly unlike our experience of the physical could be multiplied. So, if you're going to extend "matter" and "physical" to include all of reality (angels and God), then you do have a burden of proof. It's the same burden of proof faced by the idealist, just the opposite position. In short, you must show that all of reality is of one kind of substance (i.e. matter). It's a burden you have yet to satisfy. And, unfortunately for you, you will have to do some philosophy to achieve that.
it's all dismissed out of hand because a heathen philosopher named Plato didn't much care for material things.
You have rejected the philosopher without engaging his philosophy, as if what he thought was the result of some agenda against true religion. Of course, that is not the case. This is where it is not clear whether you have consider the metaphysics of physicality and matter. Since you depend on what we know from everyday experience, let's start there.
Here's what we know from our observation of physical entities. Every single one of them, without exception, come into existence and depart, and they do so on account of their dependence on other physical entities. This is contingency. If we go on observation alone, without engaging in the metaphysics involved, we would have to conclude that contingency is a necessary feature of physical entities (physical objects are contingent in all the possible worlds in which they happen to appear). I assume, correct me if I am wrong, you believe that there is at least one physical Being (i.e. God) that does not come into existence and then depart. That is, God is necessary. So, here we have a Being that is both necessary and contingent, which is a contradiction.
Why is that a contradiction?
In short, you absolutely do have a burden of proof if you are going to posit the existence of a material God. As a classical theist, I really have no idea how such a proposition would even work conceptually. Is this material God a necessarily existing being that would exist in every possible world, and if so... how? What is it about matter that would make its existence a metaphysical necessity? Did matter exist before this material God? Could the material God cease to exist?
Silmarien has already touched on the problem with your position. If something is contingent, then it does not exist in all possible worlds. The reason for this is, if something is contingent then it will only exist in those worlds where the conditions entail that allow for its existence. Contingency is a property that can only hold within a world and has no trans-world guarantee. All this to say if something is physical, and therefore contingent, then it might or might not be.
A necessary Being, on the other hand, must exist in all possible worlds. Why is that the case? Because necessity does not depend on anything contingent. Necessity has a trans-world guarantee that ensures whatever is necessary in one world is necessary in all possible worlds. So...
If an essential feature of matter is that it is contingent (and for all we know from observation it is) then if God is "matter," God is possible in some worlds and not others. Is that your position? Could it have been the case that God does not exist? I doubt that is what you think, but that is one of the stranger conclusions of your position. You may balk at my use of philosophy. But, absurd conclusions, like the one to which your position is susceptible, are pretty objectionable as well.
Your topic is interesting, but I question the
spirit in which you have engaged the topic. In particular, your ad homenim attacks towards
@Paidiske are not fitting for one who claims to know the nature of God (1 John 4:8; see post #9 which seems to me too much against the person and not the argument). Maybe the more important distinction is not that between the physical and the spiritual, but the difference between that which comes from a place of love and that which does not.