Deckard Cain has always been available in the Diablo games to offer sage advice, words of wisdom and tell of Sanctuary's involvement in the eternal fight between good and evil. The Book of Cain puts this wealth of knowledge in one place, and now Blizzard has revealed a small portion of that tome.
The Archangel Tyrael is the focus of the unveiled portion of the tome, a carrot offered by Blizzard to fans as a way to tell more people about Diablo III and interact with the "Darkness Falls, Heroes Rise" web site. With every 10 percent (Blizzard calculates through some obscure method), a new item is revealed. This portion of Cain's book was the 20 percent reveal.
Cain offers a few insights into the Archangel of Justice and his growing conflict with the Angiris Council because of Tyrael's insistence on interfering in mortal affairs and even fighting on their behalf. The excerpt talk of Cain's admiration for the angel, but colors it with the caveat that people should judge for themselves.
The 10 percent reveal was a chat with three of the key developers on Diablo 3, although the video was made more than a year ago based on comments that it was spring and they were looking to release the game later in 2011. But you can pull a few tidbits from it below.