It's located near the flickering lantern post, next to a bloody message on the wall, "HOW ALIVE ARE YOU" in the Courtyard. The document was written by Father Martin and was left for Miles to find.
"I don't even know your name. But I've come to think of you as one of my blood, my Paul, I hope you don't mind. And I hope you don't indulge the vanity of self-pity, the fear that your suffering is more than others'. We all must endure this, and you are nearly done. There's no way to heaven but by the cross. And every man needs another to help drive the nails in. I am here for you. I am waiting up ahead."