I’m looking for a book I read sometime between 2005-2011. The cover was mostly blue and had a sword hilt on it I think. In the book a kid from our world somehow goes to another world. In this other world, the people fight with swords that the blade only actually exists if you believe? Little hazy on that part. I remember a scene where the main character loses a foot race to a younger kid from this other world. The people train using the swords by swinging them at giant boulders. The sword blade can heal any wound when pressed against it unless it’s caused by that type of sword. Might have had Christian themes. When in our world the main character was attacked by some sort of invisible monster that can’t be seen. Somebody saved him using one of the magic swords.