Avacyn

Avacyn is an archangel that inhabits Innistrad, and is the central figure of the Church of Avacyn, who gives the humanity of that plane the faith to fight for survival.

The creation of Avacyn

link title The vampire planeswalker Sorin Markov created an angel he named Avacyn, and tasked her with protecting the plane. Through her, the magic of faith would create true power to fend off the darkness. The Church of Avacyn grew up around the power Sorin invested in her.

Avacyn's purpose is to maintain the balance on Innistrad. Without her the equilibrium between humanity and the dark forces would be broken, with the resulting extinction of humanity at hands of the vampires or werewolves and the triumph of the demons over the plane.

Dissapearance of Balance

The angel's disappearance has not only endangered the humans of Innistrad, it has smashed the carefully-constructed balance between humanity and the creatures of the night. Sorin knew never to expect peace and harmony on this shadowed world, but he thought he had arranged a kind of effective equilibrium, a set of safety measures designed to keep one side of the scale from tipping too far.

External information

http://www.wizards.com/Magic/Magazine/Article.aspx?x=mtg/daily/stf/177 Sorin's Homecoming