Who is Faithful. from In the Hand of the Goddess and what is their importance?

Faithful is the name of Alanna's familiar. Faithful is a cat with the same violet color eyes as Alanna. Alanna and Faithful are able to communicate telepathically. Faithful protects Alanna and warns her when danger is coming. They are friends and the cat gives Alanna advice. Faithful is always at Alanna's side and rides in a special cup on Alanna's saddle.