Guess we've finally gotten somewhere, Roswaal wants Echidna, and he follows the book Tome of Wisdom, which tells him what he needs to do, we can assume Roswaal thinks that by going along with all this crap written in the book, somehow it’ll lead him to Echidna, all the crazy shit he did, like sending people to attack the mansion, not wanting Emilia to free the Sanctuary, but at the same time wanting Subaru to free it, it’s all in the book and he’s just following it