The book of enlightenment is an item in Fear & Hunger. Its sprite is different than the other books and is colored bright yellow, signifying its difference from the other books as one of the most useful items in the game. It can either be found as a random drop from the various bookshelves present in the game, or as a hard-coded item drop found through several important locations - a room next to Le'Garde's corpse, or the room that leads to the Hall of the gods. It is also offered as one of the items by Pocketcat for trading in a human child.
The main function of the book is to save the game. This makes it extremely useful as the game itself only has two spots where the player is allowed to save, and even those are not consequence-free. It is also perfect for exploring the game's lore and various enemy behaviors by saving right before an interesting encounter or segment, allowing the player to try out various things without the fear of losing all progress.
It is only a single-use item and will disappear immediately after, use it wisely. The item is not present in hard mode, as all saving is disabled.