The Grand Maester's Proclamation is a tome found in Act V of Diablo III. Written by The Grand Maester himself, it is given to the player by a Templar during "The Templar's Reckoning" event. Obtaining the journal will add to the People Finder achievement.
During the sidequest in question, Kormac, upon reading the proclamation, calls it "damning", and says that it proves beyond all doubt that the corruption of the Templar Order goes straight to the top. It details the Grand Maester's intent to turn every citizen of Westmarch and beyond into Templars, with everything that this entails.
It reads as follows:
The day of reckoning is at hand. We will rise from the ashes of Westmarch and lead mankind into the Light! We shall have recruits by the thousands -- every citizen will be another templar added to the cause. Once cleansed by the inquisitors, they will become an unstoppable force!