The sacred Jedi texts are a collection of books that contain the original knowledge of the Jedi religion. They were formerly in possession of the Jedi Master Luke Skywalker and were placed in the tree library while he was exiled on Ahch-To's Temple island. Before leaving Ahch-To, Rey took the books with her and they are still in her possession.
The first writings of the sacred Jedi texts were done by the first member of the Jedi Order. Later, other ancient Jedi complemented the books with their writings, and future students were also encouraged to add their own knowledge. Jedi Master Luke Skywalker collected the books during his travels across the galaxy and later registered in the texts his own investigations about a Sith cultist assassin called Ochi that had found one of the Sith wayfinders that leads to Exegol.
After Ben Solo's fall to the dark side, Luke exiled himself on the Temple island on Ahch-To, taking the sacred Jedi texts with him. Luke placed the books inside an uneti tree that he used as a reading chamber, the tree library.
Many years later, Rey got the possession of the Jedi texts when she took the books from the tree library without warning the Jedi Master. During the following year, Rey studied the contents of the books with the help of a historian Resistance member and C-3PO to translate them. She also asked R2-D2 to scan the texts and store their contents in its memory for future safekeeping. She learned about the Force healing ability when she was studying one of the volumes, the Chronicles of Brus-bu, and was fascinated by this power. She used the fundamentals of the healing technique described in the book to heal the broken kyber crystal of the Skywalker lightsaber, managing to repair the saber after it had split in half during her confrontation with Kylo Ren on the Supremacy.
They contain vast knowledge about the Jedi, but a lot of the content in the texts is not readily legible, as much of it relies on metaphors and have to be translated from archaic languages.
The contents of the books include writings from the Prime Jedi besides lost Jedi wisdom and abilities. Force projection and Force healing are two abilities included in the books. They also have writings about the history and principles of the Jedi, guiding the ones that are studying the Jedi path.
The texts dive into the mysteries and myths about the Force, attempting to explain the Force throughout history. One of the volumes, called Rammahgon, has four conflicting stories about the origin of the cosmos and the Force, and the precepts derived from them. The books have a description of the Force as a twisted ribbon lining the perimeter of all reality, and that one could transit any point across the cosmos through a place called "the Netherworld of Unbeing". Additionally, they have an image of the Chain Worlds Theorem, also called Vergence Scatter, which is a theory about the existence of the World Between Words.
The sacred Jedi texts are a collection of eight books and scrolls. Their pages are made of pulp from Force-sensitive uneti trees that helped to keep them preserved from more than a thousand generations.
Several years after Luke Skywalker exiled himself, Rey travels to Ahch-To's Temple island to find Luke and convince him to help the Resistance. She hears whispering voices while she is following Luke around the island. Guided by the voices, she enters the tree library and sees that they are coming from an old collection of books on a shelf. Luke finds Rey in the library and explains that the books are the original Jedi texts, and they along with himself are all that is left from the Jedi religion.
When Rey fights Luke about the truth of Kylo Ren's turn to the dark side, she leaves the island and Luke decides to burn the books along with the tree library. However, as Luke hesitates, Yoda's Force spirit appears and summons a lightning bolt that destroys the library. Regretting his previous decision, Luke screams to Yoda to save the Jedi texts, but Yoda replies that there was nothing inside the library that Rey didn't already possess. Beside Yoda, Luke watches the tree library burning, not knowing that Rey had stored the Jedi texts inside the Millennium Falcon before leaving the island.
One year after the events of The Last Jedi, Rey still possesses the sacred Jedi texts as she continues her Jedi training. After Emperor Palpatine announced his return to the galaxy, Rey tells General Leia Organa that while she was reading the books she discovered Luke's annotations about Ochi and the Sith wayfinder that can lead to Exegol. With this information, Rey decides to seek for the wayfinder that will guide her to the location the Dark Lord of the Sith is hiding.