"...but try the spirits whether they are of God..." (1 Jno. 4:1)
"The very existence of the concept of god argues that he is." This is almost too silly to respond to. How about "The very existence of the concept of unicorns argues that they are"? or, perhaps, "The very existence of the concept of aliens argues that they exist"? Just because the human mind can imagine something does not make it real. The idea, put further in your essay, that the ability to imagine god as something greater than us is indicative of the reality of that god, has no basis in fact. It is a logical step in imagination to go from any point - say, size - and take it as far as possible - say as big as the universe, or even bigger. It is also easy for the human mind to conceive of powers that do not exist - the ability to become invisible, for example. This doesn't mean that the ability to disappear exists in actuality anywhere in the universe.
In fact, all human concepts of gods incorporate human and/or animal features and traits. This is proof that gods are MAN made - and NOT of divine origin.
The quote by Hume - "The creative power of the mind amounts to nothing more that the faculty of combining, transposing, augmenting, and diminishing the materials afforded to us by sense and experience." does not, as you seem to want to indicate, show that imagination is limited to that which we experience. Please note the "combining, transposing, augmenting, and diminishing" words in his sentence. If we understand the existence, and limits, of life, what is the imagination of a being that was never born, nor will ever die anything but an augmentation of what we already understand and have experienced? If we recognize our limitations, what is the imagination of a being that can exceed our limits to infinite possibilities anything but an augmentation of our own experiences?
I'm going to leave the "first cause" argument for later. Let's stick with this for now.
And BTW, if you give me the challenge e-dress, I can simply copy my stuff to the list, you can copy your response to the list, and thus you will be saved having to resend everything.
CHALLENGE is published quarterly by Challenge Publications.
Jerry D. McDonald, Editor; Michael P. Hughes, Associate Editor.