Coming as this episode does in the opening chapter of the novel, this is one of many episodes of debased artistic performances in the novel. The twins later on become irritating in many ways, not least for their amateur and unsophisticated musical renditions, but let us also note the way in which their choice of music foreshadows what is to come in the rest of the novel. The opera from which the music they play is drawn deals with the story of Zampa, a pirate chief in the seventeenth century in Sicily, and how he sets in motion a romantic plot of love, betrayal, violence and death in the sea. Clearly therefore such a choice of music is richly telling, focusing as it does on the setting of the sea and the way that this tale of love and treachery will be told with this backdrop. The parallels between this tale and the unfolding drama of Edna herself are clear, especially the central role of the sea in Edna's tragedy.
This scene is meant to create not just foreshadowing, but also the overall sense of mediocrity that looms around Edna's life. While she has all that she needs in life, she clearly has not lived up to any expectations except for those which are forced upon women by society. As a result, what could be taken for a "good life" is seen through her eyes quite differently: it is minimal, boring, worthless, and coarse.
So is this scene. On one end you have Mr. Pontellier enjoying his cigar, people playing croquet and on the other end we witness the Farival twins playing that duet from Zampa. At the same time, Madame Lebrun is shouting out orders back and forth and, in all, the atmosphere is both uncomfortable and somewhat noisy and chaotic.
The foreshadowing comes from the music itself. Zampa deals with the story of a lover who dies at sea. As we know, Edna will "give herself up" to the ocean at the end of the novel, understanding that love, as she knows it and thinks of it, will never manifest in a way that would meet her hopes or expectations. We learn how passion, love and romance were not exactly well-defined in her mind
She was a grown young woman when she was overtaken by what she supposed to be the climax of her fate. It was when the face and figure of a great tragedian began to haunt her imagination and stir her senses. The persistence of the infatuation lent it an aspect of genuineness. The hopelessness of it colored it with the lofty tones of a great passion.
Therefore, the choice of Zampa and the backdrop of the scene bring out the inner turmoil in Edna's life; that uncomfortable and unresolved want for "something" that is never there. A background noise that bothers her consistently and she manages to silence with her own death.