Interaction between Christianity and other religions in a juvenile novel

Nancy Farmer is a prominent writer of fantasy literature for young people. She is a good writer, and, among other things, takes religion seriously:
Anyone who studies psychology, as I did, knows that psychology is pretty close to magic. I'd also studied religions, and so I also knew that religion gets into questions that science can't pin down, and that have their own validity. Nancy Farmer, interviewed by Leonard S. Marcus, in Marcus's The Wand in the Wind: Conversations with Writers of Fantasy. (Cambridge, MA: Candlewick Press, 2006) Interview is on pages 49-61. Quote is from page 56.

In Farmer's The Sea of Trolls (New York: Simon & Schuster, 2004) there are three religions. They are Catholic Christianity (The book is set in eighth century Europe), the religion of the Northmen, and druidism. Jack, an Irish peasant boy who has been raised by a Catholic father and a Druid mother, is kidnapped by Northmen, and, eventually, becomes a hero in their eyes and returns to his home and parents. He comes to see Olaf Onebrow, a war leader, as truly brave, honest, and generous, but cannot condone Olaf's treatment of slaves, or the Norse custom of killing a wife and putting her on the funeral boat to be burned when a warrior dies. Jack especially dislikes the Norse notion of reckless abandon in battle (and taking other risks) as a way to achieve glory in the after-life.

Here's one conversation:
". . . When Odin wanted the lore that would make him leader of the gods, he had to pay for it with suffering. He was stabbed with a spear and hanged for nine days and nights on the tree Yggdrassil."
"That's just plain stupid," Jack said.
"Your god was nailed to a cross. It's the same thing."
"No, it's not." (p. 301)
The conversation is with Thorgrim, a shieldmaiden who is about Jack's age. There are other conversations contrasting Christianity and the Norse religion, for example on pages 126 and 186. I have to agree with Jack here. Christ already had all the wisdom that He needed. He died for us.

I found no such discussions comparing Christianity and the Druid religion in the book.

There was also this great statement:
"I have lived long enough to know that nothing lasts forever. Such joy as Olaf's will sooner or later attract its destruction. But I also know that to ignore joy while it lasts, in favor of lamenting one's fate, is a great crime." (199) The speaker is Rune, a Norse Bard, to Jack.

I won't give the plot away further, except to say that it was a good one, and not only in plot, but in characterization and setting. Farmer claims to have done considerable research for this book, and it shows. She well deserves the honors she has achieved as a writer.

Thanks for reading.