When he's not killing people, Judge Holden likes to sit with his personal ledger and write down all kinds of things and people he's come into contact with. As the narrator says at one point:
In his lap he held the leather ledgerbook and he took up each piece, flint or potshed or tool of bone, and deftly sketched it into the book. (11.11)
His fellow gang members are skeptical though about his ability to copy down every single thing in existence. As one dude says:
But no man can put all the world in a book. No more than everything drawed in a book is so. (11.13)
At the end of the day, though, the judge is completely undaunted.
When asked why he writes everything down in his book, the judge answers:
Whatever in creation exists without my knowledge exists without my consent. (14.61)
In other words, the judge thinks of himself as a godlike figure who gets to decide what deserves to exist and what doesn't—from rocks and plants to human beings. You can call him crazy, but by the end of this book, the judge is the only man left standing. It makes you think.