That’s because, as an overwhelming surprise, Palpatine will be returning to the Star Wars story after departing the series in Star Wars: Return of the Jedi. How? Last time we saw him, he was tossed down a very large hole by his protégé, who appears in this scene. Him telling the legendary story of Darth Plagueis, and revealing his interests in immortality, likely will be important to the character’s resurrection in the upcoming movie.
Article source: https://www.cinemablend.com/news/2485758/jj-abrams-has-revealed-his-favorite-star-wars-prequel-scene