The Priors give Adria two books. One is THE Book - the Book of Origin. The other is the diary of Neelis, a heretic.
“Read this one first,” they tell her, indicating the holy book.
She is the will of the Ori, but she is still young, and in need of guidance, so she does as they ask.
In the Book of Origin she finds comfort, strength, purpose, understanding. The diary she finds confusing, and it makes her angry. Why would anybody reject the teachings of Origin?
“Why did you want me to read a heretic’s diary?” she asks them afterwards.
“So that you will be familiar with the rhetoric of those who oppose Origin, and be prepared to counter it,” they answer.
Quick research in the archives reveals that Neelis was burnt on the ara, a sacrifice to cleanse his soul and increase the power of the Ori. Adria’s mother was burnt on the ara as well, but survived.
Adria wonders if her mother ever read Neelis’ work. She wonders if Vala ever wrote her own. She wonders if she herself is doomed to burn. After all, if Adria’s words can’t sway Vala, how can they convert a whole galaxy?