What is the importance of "the sword" in the novel, Turned (Book #1 in the Vampire Journals)?

The sword, a supposedly mythical object spoken about for millennia by vampire lore and Doctrine. Doctrine holds that this sword shall be found by the chosen One, whom Caleb believes is Caitlin. It is believed that the discovery and use of the sword will avert a catastrophe of apocalyptic proportions for both vampires and humans alike. Caleb fervently believes the sword exists, while most in his coven believe it to be only a legend.