But ballet is always devoid of dialogue

Even so, it still manages to tell a story, and that story is echoed in the rest of the film. The ballet is the culmination of the artistic creation of a group of people which is one of the main strands of the story. The efforts and dedication that people put into a work of art, and what it can cost them.
From the Powell & Pressburger canon more people usually mention
A Matter of Life and Death and its courtroom scene. Although I find that to be a very clever discussion many people think it slows things down too much and spoils their enjoyment of the film.