The True Revelation is a relic that can be found in The Darkness 2. It is an attempt to decipher "The Revelation of John", the last book of the Bible.
According to Johnny Powell, there are three different interpretations of the Revelation of John: as a literal prophecy, as a metaphor for Roman persecution, and as a code that can reveal the True Revelation when properly deciphered.
The people who believe that the Revelation of John can be deciphered do it differently, which is why each copy of the True Revelation is unique. This particular copy was written by the Brotherhood and predicts their fall into madness.