I am hesitant to spoil the series, but I will do so in order to more fully be able to speak about it. Beware those spoilers, because they’re going to be big ones.
Lyra is a young, preadolescent girl. Her soul exists outside her body. It has a will and a mind and a name of its own, but it’s still her soul. It can take on the shape of any animal, and it can talk.
Everybody in her world has one of these animal companions, called a daemon. Childrens’ daemons have no set shape, and can change form at will. Adults’ daemons have a set animal shape that in some way illustrates or reflects the owner’s personality. It is considered unspeakably taboo to touch another person’s daemon. This becomes obvious later in the series.
Kids and daemons alike have no idea when or how their daemons will pick a shape and stay with it – Lyra and her daemon, Pan, just assume that he’ll pick one when he feels like it.
But very late in the very last book, we learn how and why and when a daemon picks its final form – it is touched by the owner’s first lover. This is why it’s taboo to touch another person’s daemon, because the act of doing so is highly sexual in nature. Instead of shaking hands with a man you meet, it would be like sticking your fingers in his mouth.
This is the central point around which the book pivots, and there are hints to this throughout, finally coming to fruition when the main character, Lyra, fulfills her destiny and becomes a second Eve – bringing about the “fall” by having sex and falling in love. Through this, she saves the mutliverse.
But not quite. To really save the whole universe and the free will of humans and the creativity and sentience of our entire species on every world and in every universe, she and her first and greatest love can never be together. They get a few days together, but that’s all – they have to split up and live in separate universes, never again able to communicate.
His Dark Materials is about growing up. Growing up is about falling in love, but it’s also about having your heart broken. Being an adult is simultaneously reveling in the bright brilliance of life’s greatest joys while accepting that every one of them is finite, and that things end. Life and death, joy and sadness, all that stuff.
I’ve read a lot of books about growing up and coming of age, and I’ve even written a few stories about it, but few writers have captured it as well as Pullman has.
I’m not just saying that because he’s an atheist, either, or because he’s written an atheist answer to The Chronicles of Narnia. He’s also written a literate answer to The Chronicles of Narnia, and an educated one, and a clever one.