I'd like to add to my original take of using myths and fairy tales in stories to enhance a new work. Back so many years ago (ok, it was 2004) and I was a young, beautiful (sleep deprived, beer swilling) college grad, I wrote my thesis on C.S. Lewis's Till We Have Faces. (It wasn't my first pick, but my advisor wouldn't let me do Chronicles of Narnia on the basis that it was overdone...and when I tried to come up with a thesis on it that hadn't been written before, I couldn't.)
For those of you who don't know this little-known work, Till We Have Faces is Lewis's only fantasy written for adults, not children. It's based on Apuleius's myth in the book The Golden Ass...a myth more commonly known as "Cupid and Psyche." If you don't know the myth, well, I'm just shocked, and you can find a summary here.
Anyway, Lewis wanted to take this very pagan myth and "Christianize" it (that's the whole point of my thesis, btw). He tells it from the "wicked" sister's point of view (although she's not that wicked...most of the story is about how the myth has been skewed by misunderstanding). He changes the story to show that Psyche is like a chosen one from God, and how difficult it is for those who are not "natural" saints to accept and love those who are; how sometimes our love can be more like jealousy, and we sometimes bring down the people we love because we don't want to them to leave us.
It's a brilliant book. But it's not a repeat of "Cupid and Psyche." The story isn't about love conquering all...or least, it's not about human love conquering all. Lewis changed the purpose of the story, and that changed everything.
That's the point of using a myth as a jumping off point or inspiration for a new story: to create an entirely different, new story.