I haven't read the book in a couple of years, but I remember the island as made of some spongy vegetative life form, which desalinated the water as for a pitcher plant effect. I didn't bother to torture the allegory to fathom what it alluded to religiously. Maybe atheism? (It seems comforting or even salvation, but ultimately it is the deceptive consumptive of the soul. I dunno.) I thought it was engaging in parts.

By the end I wanted the book to be a person so I could say, "Fuck you, book. I believe in God even less now."