Here's why:
* Prior to "The Jazz Singer," there were movies with sound effects and musical accompaniment, but these were played live in theaters.
* "The Jazz Singer" was a partial talkie, meaning it had some dialogue, but not the whole film. It was also a silent film that used the Vitaphone system, which synchronized sound on a phonograph record to the movie.
* "The Lights of New York" (1928) is often cited as the first *full-length* talkie, but it was released shortly after "The Jazz Singer."
So, while "The Jazz Singer" wasn't the absolute first movie with any audio, it's considered the first to successfully combine synchronized sound and a narrative film, marking a major shift in cinema history.