There are three different themes seen in Guy de Maupassant's short story "The Necklace": Appearance and Reality, Class Conflict and Generosity and Greed.
Through Maupassant's use of a third person omniscient narrator (a narrator who simply states the action of the story without involvement or judgement), he impresses upon the reader a sense of dislike for those who try to be something they are not.
The narrator simply states the character of Madame Loisel, her views upon her social ranking, and what she is willing to do to feel a part of the class which she so desperately wishes to belong to. The narrator's stand, therefore, is one which fails to connect with the characters (which could tend to sway the reader).
The author tone is shown through the voice of the "removed" narrator. Without having the narrator actually involved with the characters, Maupassant allows readers to judge for themselves the characters depicted in the story (given the narrator has no direct impact upon the reader). Through this, Maupassant is showing his own tone regarding the greedy and manipulative. Essentially, Maupassant finds the greedy and manipulative interesting enough to construct a story about them (while teaching to accept what one has), but he does not "like" them enough to move them using a tone which could connect the reader to the characters (other than the pity one may have for M. Loisel given his wife forced their poverty).
Using an ironic tone, the author makes us feel bad for the main character. For example, he writes,"She was one of those pretty and charming girls born, as though fate had blundered over her, into a family of artisans." The entire story is also centered around the main character trying to replace a diamond necklace that she had lost. As soon as she uses all of her money and buys the necklace, she finds out that the original one was fake and worth less money that the one she bought. It's ironic, because when Loisel gets wealth, she loses it for nothing.