Matter and God
Berkeley’s philosophy is built around the idea that matter and God are inconsistent with each other so we need to remove matter from our metaphysical view. The reason for this is that matter encourages skepticism, both about the external world and about God himself. If the world consists of matter, then there are insurmountable problems about our knowledge of it; and if matter is the cause of our sensations, then there is no place for God in the workings of things. Thus we can rationally doubt that matter exists, or that we know its nature; and we can worry that God has been metaphysically sidelined. Berkeley’s own immaterialist philosophy obviates these problems by (a) locating objects firmly in the mind and (b) making God the cause of human experience and all other events. Matter is no longer what we perceive when we perceive things (even indirectly), and it is no longer the cause of what happens: for it has no existence whatever. We perceive ideas in our minds, and everything ultimately resides in the infinite spirit that is God’s mind. According to this metaphysical system, skepticism gets no foothold, since there is no gap between experience and reality, and because there is no danger of God’s redundancy. We also avoid questions about how an immaterial God could create matter, about how matter can have active powers, about whether the nature of matter can be grasped, and about how matter can be defined. All the problems bequeathed by Descartes, Locke, Gassendi, Malebranche, and others are swept away in one stroke; in particular, skepticism, both about the external world and about the teachings of religion, is decisively vanquished. Berkeley’s underlying reasoning is simply that matter leads to skepticism so that it must be removed for skepticism to be defeated. A purely immaterial world, on the other hand, consisting of ideas and spirits, finite and infinite, is a skepticism-proof world, and hence a world in which God’s existence is assured. We need no longer fear that skepticism undermines God’s wisdom and benevolence, leaving us hopelessly adrift in an ocean of doubt, reliant on mere faith to save us from the epistemic abyss. 
This is a coherent and in many ways attractive story: the denial of matter certainly helps ease the threat of skepticism about objects and about God. For now we have immediate experience of objects, and God is essential to the universe as the ultimate cause of everything that happens. God steps in to do what matter was alleged to do, but without the problems inherent in the materialist position.  But Berkeley’s position depends on a prior acceptance of common sense and religion: we already have to be convinced of these belief systems in order to do what is necessary to save them. Can’t we contrapose Berkeley’s argument to derive the conclusion that God does not exist? That is: if there is matter, then there is no God; but there is matter; so there is no God.  For if matter exists, then skepticism is real and unanswerable (despite various heroic efforts); but God would never create a world in which this was the case, so there is no God. Why would God create a universe in which reality is so out of epistemic reach, and in which his own existence has so little rational foundation, when he could create an immaterialist universe to Berkeley’s specifications, in which skepticism is impossible? So the existence of matter, and with it the materialist metaphysics of “sensible objects”, is a reason to doubt that God, as traditionally conceived, exists at all. Berkeley is quite correct in his reasoning—matter and God are inconsistent—but the indicated conclusion is that there is no God. To put it baldly: the existence of matter entails the non-existence of God. That is basically what Berkeley believed, but he thought he had a viable alternative to matter, unlike the philosophers he contended with. But if we can’t stomach his idealism, we have to draw the conclusion he was so keen to avoid, viz. atheism. Berkeley was right: matter leads inexorably to atheism—but the correct inference is that atheism is true. He had a clear sense of the lie of the metaphysical land, but he drew the wrong conclusion. A world of matter (even conjoined with Cartesian immaterial minds) is not a world in which God can happily exist, because of the skepticism it generates, both about itself and about the place of God in the great scheme of things. Matter is essentially anti-God.
You may reply that we could just accept Berkeley’s own view and reject matter, thus avoiding the inevitable atheism he so feared. That depends, however, on whether his metaphysical system is internally viable. I won’t go into this question here, but two points may be noted. The first is that Berkeley was much concerned with a certain fact about perception that apparently conflicts with his position, namely that objects appear to exist at some distance from the perceiver. The materialist has an account of this—material things are laid out in space relative to the perceiver—but what can the immaterialist say? Shouldn’t the objects of perception appear to be in the mind, which is where they actually are? It might be replied that we are under a perceptual illusion about their location, but then we are back with skepticism: how could God have built us in such a way that our every experience contains an error that invites the false belief in materialism? Berkeley struggled with this problem, and the problem is certainly real. Second, there is this question: what about other sorts of skepticism? Berkeley focuses on skepticism about the external world, but that is not the only kind of skepticism there is—what about skepticism concerning other minds, or the past, or the future? These forms of skepticism are not undermined by the immaterialist position, so skepticism still afflicts us even assuming Berkeley’s metaphysics. There is still a problem about reconciling God’s existence with the specter of skepticism. Berkeley’s system does not free us of skepticism, after all; it merely dulls the edge of one form of it. Any form of skepticism is a threat to the existence of God, as he is traditionally conceived, so it won’t suffice to banish one form of it. So Berkeley’s metaphysics doesn’t really do the job it is supposed to do and it has internal problems of its own; we can’t just cheerfully adopt it and leave the way clear for belief in God. Accordingly, we must accept that the truth of materialism about “sensible objects” poses a problem for theism, just as Berkeley supposed. His great contribution was to see that matter and religion can’t peacefully coexist. The corporeality of tables and chairs is inconsistent with the existence of God. 
 Here is Berkeley early on in the Principles of Human Knowledge: “We should believe that God has dealt more bountifully with the sons of men, than to give them a strong desire for that knowledge, which he had placed quite out of their reach.” (Section 3) Why torment us with being knowledge-desiring beings whose desires can never be satisfied? That would be like making us food-desiring beings but without the ability to eat. God is not capable of such cruelty or ineptitude.
 Note that materialism here is not the general doctrine that everything is material (including minds); it is the more limited doctrine that the objects of sense are material. In this sense Descartes counts as a materialist (about the world of mountains, rivers, trees, etc.).
 Strictly, we should not say that there is matter in the classical sense of extended substance, since it is doubtful that there is any such thing for reasons deriving from physics (see my “Is Matter Intelligible?”). Instead we should say that there is something non-mental and existing outside the mind: this could be energy or fields of force or objective space or whatever basic stuff composes reality. We could even include psychic entities of the kind postulated by panpsychism, since these are equally anathema to Berkeley, being liable to skepticism and not present to the conscious mind of man.
 It took a genuinely religious man, of remarkable sharpness of mind, to see that his religion was threatened by such a seemingly innocuous assumption. In effect, he came up with a startling disproof of God’s existence, contrary to his intentions.