Thoros of Myr said, "According to prophecy, our champion will be reborn to wake dragons from stone and reforge the great sword Lightbringer that defeated the darkness those thousands of years ago."
According to prophecy, in ancient books of Asshai from over five thousand years ago, Azor Ahai is to be reborn again to challenge the Others. This will occur after a long summer when an evil, cold darkness descends upon the world.It is said that wielding Lightbringer once again, Azor Ahai will stand against the Others and if he fails, the world fails with him.
Here's one of my theories, based on Westeros history, the books, and what we've seen D&D "change" from the books:
The sword that fat Sammy stole from daddy is, in fact, LightBringer.
He'll end up delivering it -- maybe through Jorah Mormont coming to the Citadel looking for a greyscale cure -- and it will end up in the hands of Daenerys.
(I think he breaks the sword fighting his father, and the Red Priestess over there -- in Mereen -- will reforge it. Heh, it would be cool in Gendry reappeared to do the smithy work...)
Although it says "he", it could be that "she" will become Azor Ahai!