This forest eats itself and lives forever. (1.Prologue.2)
The forest is like a real life Ouroboros. Infinity is possible, but not without death and rebirth.
Book 1, Chapter 7
"Where you'd be wearing out the knees of your trousers, sir, they just have to go ahead and wear out their knees!" (1.7.16)
In the Congo, bodies are like tools. They're used and abused, and some damage is irreparable. It's not a bad thing; it's just the way life is.
Book 1, Chapter 10
Adah Ellen Price
If God had amused himself inventing the lilies of the field, he surely knocked His own socks off with the African parasites. (1.10.37)
It's easy to forget that we're not the only creatures on this planet. There are millions of them that we can't even see. Does their size make them unimportant? Not to Adah—but definitely to Nathan.
Book 2, Chapter 1
Childhood was nothing guaranteed. It seemed to me, in fact, like something more or less invented by white people and stuck onto the front end of grown-up life like a frill on a dress. (2.1.41)
Childhood is a man-made concept. In the Congo, everyone has to pull his or her own weight once they can walk on their own. It's like being a Boy Scout without the merit badges or the adult supervision.
Book 3, Chapter 5
"Everything has to eat something." Even lions, I suppose. (3.5.12)
Adah shrugs off almost getting devoured by a lion. To her, it's all part of the natural way of life. Who is she to deny a lion a good meal?
Book 3, Chapter 8
"When I want to take God at his word exactly, I take a peep out the window at Creation. Because that, darling, He makes fresh for us every day without a lot of dubious middle managers." (3.8.24)
Brother Fowles, a preacher himself, doesn't really believe in preachers as evidence of God. He believes in the everyday miracles of nature.
Book 3, Chapter 21
"We all get hungry. Congolese people are not so different from Congolese ants." (3.21.12)
Anatole takes an attitude similar to Adah here: even ants have to eat. And as we see later, the humans are like the ants when they do their hunt. They burn the ground, trap the animals, and strip them of their flesh.
Book 4, Chapter 3
Adah Ellen Price
The death of something living is the price of our survival, and we pay it again and again. We have no choice. It is the one solemn promise every life on earth is born and bound to keep. (4.3.12)
This is Adah's observation after the hunt, and this is probably why she had a so-what attitude about the lion. If humans will kill and eat animals without a second thought, why shouldn't animals be allowed a fair crack at humans?
Book 5, Prologue
My household would pass through the great digestive tract of Kilanga and turn into sights unseen. (5.Prologue.1)
If you don't get eaten by lions or ants or snakes, you can still get eaten by the jungle itself—and transformed in the process. At least Orleanna's still alive at the end of it.
Book 6, Chapter 1
Rachel Rebeccah Price
The way I see Africa, you don't have to like it but you sure have to admit it's out there. (6.1.20)
Here's Rachel, once again demonstrating her legendary acceptance and tolerance/snark. You can replace "Africa" with "nature" here and get a similar result. It's out there, and whether you like it or not, you'll be a stronger person if you can learn to live with it.