The sacred Jedi texts were a collection of books and scrolls kept within a uneti tree near the first Jedi Temple on the aquatic planet of Ahch-To. They were said to contain ancient scriptures, including the Aionomica and the Rammahgon, lost Jedi wisdom, and abilities.
"The Force is the light, the Force is the dark. Jedi choose the light, for all it reveals."
―C-3PO reading a passage from one of the texts