Brandon's discussion of substance got me thinking about metaphysics and I thought of something that I think might work. If you guys are familiar with this already, I'm sorry for reexplaining it to you, but here is the quick and dirty version. Aristotle argued that the most basic metaphysical principles, of which all existing things were constituted, were form and matter. For Aristotle, form was the "that which makes a thing that which it is", that is to say, a dog is a dog because it has the form of a dog and a human is a human because it has the form of a human. Now, form doesn't mean shape, it's an immaterial metaphysical principle. Matter, on the other hand, is a lot like what we think of as matter. It is the material aspect of things. Matter is informed by forms and these two metaphysical principles work together to make things what they are. Now, Aristotle, and later St. Thomas, thought that both of these metaphysical aspects of created being were of equal importance. Take a human being, for example. Both Aristotle and Aquinas identify the human form as a special kind of form and thus call it the soul. Now, because one might tend to place more emphasis, when considering humans, on the mind, on our capacity for rational thought, which flows from our souls, because it is what separates us from all other animals. Or, one might tend to give too much emphasis to out material aspect because we are bodily creatures and everything we interact with is material. Both Aristotle and Aquinas, however, would think that both of this positions are incorrect. They would say that it is our very nature to be a unity of both the material (matter) and immaterial (form). Finally, as an aside, neither Aristotle nor Aquinas was a substance dualist because they thought that neither forms nor matter (in its uniformed state) were substances in themselves.
Okay, so what has this to do with anything. Well, what if the Abos and the Shadow Children are supposed to be representatives of these two philosophical extremes? What I mean is, perhaps the Abos are meant to represent the person who puts too much emphasis on the material, and therefore, doesn't ever really know what they truly are, hence the constant shape shifting. They would be a personification of the existential axiom "potency precedes act" that we find in Sartre. The Shadow Children, on the other hand, would be representative of the other extreme, people who place too much emphasis on immaterial, that is to say, the mind. The Shadow Children say thought is all that matters, but this is patently false, actions matter, the fact that we have a body matters, and the care for it matters. This is why ethics exists as a science exists at all. This would, I think, place Sandwalker in the middle, perhaps as someone who has the proper relation to the different aspects of his metaphysical make up. We would see this represented by him interacting with the land in a proper and respectful way and in being able to become a Shadow friend. In other words he is able to live in both worlds well, and not become too far given over to one or the other of them.
Anyway, I think there is probably a little more massaging of this idea to be done but I it seems like it might be a pretty good potential read of it. It would also map well onto the idea of this second section of the story being the Purgatorio of the book since it is in the Purgatorio that we see both of our metaphysical principals working most closely together. What I mean is, in the Purgatorio, we see people happily enduring physical mortifications in order to effect spiritual cleansing. This wouldn't make any damned sense unless the physical and the immaterial had some kind of relationship in the human person.