Eris carries forth Toland's teachings of "use the darkness as a weapon, for it is the winning strategy". She was locked in the moon for years, with only Toland's writings and advice for company as she was hunted, tortured and warped. With the opportunity to create a weapon, through the methods of her fallen Warlock fireteam member, she encourages you to seek out these materials in order to strike back at the Hive with all the hurt and malice that she suffered through. It's the lore of the worms being utilised by a slightly insane Eris.