The trouble with definitions of god is that they tend to get mired in semantic debate: omnipresence versus pantheism, transcendent but immanent and so on and so forth, not to mention the impossible debates surrounding good and evil. I doubt that any two practitioners of any faith have exactly the same idea of god in their heads, at least if they’re being honest and not just repeating what they may have been told by someone else. The non-canonical Gospel of Thomas, found in the 1940s, buried in the sands of Egypt for centuries, sheds some interesting light on what some early Christians may have believed and it is quite surprising for sure.
Anyway, getting back to the point. What purpose does myth serve?
I think that there are myths and there are myths, so to speak. There are myths that may have once served as mnemonics for practical purposes, but their metaphors are so ancient and there original contexts so divorced in time from our own that we have lost the ability to understand them without doing some serious digging and even that leads us inevitably to speculation or conjecture. I’ve read some interesting materials in recent years about how constellation names and star-lore, something which might interest you, may go back to the Stone Age and be connected to seasonal hunting patterns; some cave paintings in France, I believe, have been convincingly interpreted as mapping out the stars. The other group of myths, in my opinion, are also full of lost metaphors, but are more metaphysical and connected to teachings and truths to be revealed – they should never be read as prose. The Fourth Branch of The Mabinogi is an interesting case in point, from what I’ve read and reflected upon myself, it’s about many things far beyond turning into eagles and owls. Interestingly enough, the actual origin and etymology of the Greek word mythos is unknown, itself shrouded in mystery, something which I find quite poignant too.