This is probably my favorite chapter of the entire book, but nevertheless I'm going to try to restrain myself from expostulating too long upon it.
First, as a preface, note that this chapter is split between excerpts from the fictional book that the protagonist Anodos is reading and sections written by Anodos in first person.
The opening paragraph is fascinating to me. Essentially what the author (of the fictional book) is writing is that there is an interconnectedness in the world and in the universe at large that is beyond the physical, scientific or natural. While the most concrete example is certainly natural, that the matter of the earth (iron, copper, gold, carbon, etc) is actually the result of ancient fusion and supernovae in various stars, yet the author insists that this is merely an example of some greater principle. He says that there must be more than "a common obedience to an external law", that "the blank" (in the past) and the "misty spendour" (in the future) may reveal even more relations to creation at large (other planets and stars) than science or poetry can tell us.
What these deeper connections might be, he does not say and I cannot fathom. But he is arguing from an almost inductive stance, that humanity has learned tremendously about the interconnection of life on earth (the so called "web of life"), interconnection to the environment and even to other planets in the solar system (indeed, we would not have tidal forces without the moon), that by induction one can assume these interconnections must continue into the deeper and more exotic places in creations.
I can't agree or disagree, I just think it's an interesting thought, and it's one that is implicitly referenced in the story when the author suggests that children are born in our world (the Earth) when people die in this other, unnamed world.
I'm also fascinated how the world has seasons that change so much more slowly. It seems almost prophetic in the story to think about a woman who might be born in fall or winter and grow up, yet never live to see the spring. How that must burden the heart, to never experience warmth and growth and new life!
I absolutely adore the narrator talking about how he tried to describe sex to the men and women there, how he tried to avoid the topic as much as possible and was eventually forced to describe sex in the "vaguest manner I could invent".
The rest of the story is amazing, but MacDonald tells it better than I do, so I will leave it to him.