I'm just gonna reiterate my last post in a TL;DR form here, since no one seemed inclined to comment on it very much.
Gnosticism is the belief that
a. there is a division between spiritual world and material world, and
b. the spiritual world should be embraced, even at the cost of losing sight of the material world.
Agnosticism, then, is the antithesis of Gnosticism in a similar way that Atheism is the antithesis of Theism.
Agnosticism is a world view that
a. is not certain whether there is a division between spiritual and material world, but acknowledges it is a possibility, but
b. it is not worthwhile to concentrate on the spiritual world
at the cost of material world since we have no reliable information on it.
These terms do not fit on the same axis as Theism - Atheism (and different variations of them such as Pantheism, Polytheism, Monotheism, Antitheism, Materialism, Physicalism, etc.).
Gnosticism/Agnosticism axis describes the general opinion on how important is it to focus on the spiritual world, regardless of what a person's particular beliefs on that spiritual world may be.
As an interesting curiosity, the ancient Greeks had a very fascinating view that everything in the unicerse, or
cosmos, was governed by the same set of rules (with exception of Chaos, of course). In fact, the world cosmos means...
...orderly or harmonious system. The word derives from the Greek term κόσμος (kosmos), literally meaning "order" or "ornament" and metaphorically "world",[1] and is antithetical to the concept of chaos. Today, the word is generally used as a synonym of the Latin loanword "Universe" (considered in its orderly aspect).
What the Greeks believed was that their "Deities" were governed by the exact same cosmological rules as humans, animals, and other mundane things. The only difference between the Greek gods and humans, then, was basically the level of ability and power to do things that normal humans could not. And the scale from "mundane" to "divine" was a continuous spectrum, rather than a clearly-defined limit somewhere.
Similarly, for the original hunter-gatherer peoples, it seems that their religion was concentrated on natural spirits and totems rather than omniscient, omnipresent and omnipotent divine figures. These things were
part of the natural world for them.
In fact, I would argue that the aforementioned definition of "God" popular particularly with the monotheistic religions is a fairly new invention and likely coincided with the formation of organized religions - possibly influenced by the birth of cities, where the rulers occasionally would claim their authority to be divine, elevating themselves to divine status (Pharaohs of Egypt, Kings of Uruk/Sumeria/Persia, Emperors of China and Japan etc.).
My rejection of theism is more of a conceptual than ideological. It stems from my basic world view which basically says that whether or not we can explain some thing, by existing it is still a natural part of the universe, and as such it is impossible for me to classify anything as "divine". That's why, should any entity make its existence known to us that would seem "divine" or even claim itself to be of divine origins... quite frankly, I would still not accept them to be "divine" by the virtue that they would exist in the natural universe.
That's why I can't describe myself as either gnostic or agnostic, since both of those require at least acknowledgement of a
possibility that a "spiritual world" exists. I do not acknowledge that possibility.
In the same vein, I would describe myself as an Atheist, and specifically Materialist, Physicalist, and probably Antitheist as well.