Will is the bearer of the knife. Now, accompanied by angels, his task is to deliver that powerful, dangerous weapon to Lord Asriel - by the command of his dying father.
But how can he go looking for Lord Asriel when Lyra is gone? Only with her help can he fathom the myriad plots and intrigues that beset him.
The two great powers of the many worlds are lining up for war, and Will must find Lyra, for together they are on their way to battle, an inevitable journey that will even take them to the world of the dead...
As a passionate believer in the democracy of reading, I don't think it's the task of the author of a book to tell the reader what it means.
The meaning of a story emerges in the meeting between the words on the page and the thoughts in the reader's mind. So when people ask me what I meant by this story, or what was the message I was trying to convey in that one, I have to explain that I'm not going to explain.
Anyway, I'm not in the message business; I'm in the "Once upon a time" business.