What is the importance of the Black Moon Festival in the novel, Kingdom of Souls?

The annual Blood Moon Festival is an annual gathering of all of the tribes that takes place at the beginning of the novel. Its importance, however, lies in what it reveals to the Arrah and the other characters. First, this is the place where Arrah finally feels Heka’s magic, but does not actually receive it. This is also where Arrah, her Grandmother, and Oshee learn of the green-eyed serpent that is clinging to Arrah. This pushes her to desperation as she yearns for magic to protect herself, providing the basis for the conflict and Harrah's motivation for a majority of the novel.