If a supernatural being is to be exempt from natural law, then it cannot have specific characteristics. Those characteristics would impose limits and those limits would restrict the capacities of that supernatural being. A supernatural being would be subject to the causal relationships that mark natural existence, which would disqualify it as God.
So we must somehow conceive of a nonspecific being without a specific nature, a being that is nothing individual, specifiable, particular, or definite. But that lack of characteristics is incompatible with the notion of existence itself. To be, is to be something as opposed to nothing. And to be something is to be something specific.
If God is to have any characteristics, which God must have to exist, those characteristics must be specific. But to assign definite characteristics, to say that a being is this as opposed to that, is to limit the capacities of that being and to subject it to the uniformity imposed by those capacities.
If a supernatural being is to differ in kind from natural existence, it must exist without a limited nature, which amounts to existing without any nature.
To talk intelligibly about God, we must assume that God has characteristics by which that being can be identified. But once the idea of supernatural existence apart from the limitations of natural law is introduced, we thereby exclude the possibility of assigning any definite characteristics to that being, because by doing that we bring our God within the realm of limitations and so within the realm of natural law.
The believer says that God transcends human understanding and is unknowable. But if one believes in God, but does not know what God is or what it is that one believes in, then that belief that God exists is a completely worthless claim and does not differ from no belief at all.
One cannot know that something exists without some knowledge of what it is that exists. To deny all the qualities of a being is equivalent to denying that being itself. A being without any qualities is one which cannot become an object to the mind, and that kind of being is virtually a non-existing thing.
If God is completely unknowable, then the concept of God is completely without content and the word God is a meaningless sound. To say that God exists, where the word God represents an unknown, a blank, is to say nothing. It's on a par with the statement that unies exist or a blark exists.
By refusing to state the content of one's belief, one exempts oneself from reason and so from serious consideration. To claim the existence of something which by nature cannot be known is to submerge oneself in hopeless contradiction.
If God cannot be known, then God cannot be known to exist. To claim that a thing is unknowable, one must first know that it exists. But in that case, one already has knowledge of it to that extent. To assert the existence of the unknowable is to claim knowledge of the unknowable, in which case it's not really unknowable after all.
When one claims that something is unknowable, if one cannot produce knowledge in support of that claim, then one's assertion is arbitrary and without merit. If one can support that claim, then one has accomplished the impossible, by having knowledge of the unknowable.
--Redacted from Atheism: The Case Against God, by George Hamilton Smith, pages 43-44.
