The tone of “A Simple Heart” is primarily a compassionate one. The narrator stays close to Félicité’s perspective for most of the story, sometimes even channeling her thoughts directly. This stylistic choice—called “free indirect discourse”—signals that a narrator feels sympathy for a given character, as they open up to experiencing said character’s thoughts and feelings directly rather than merely reporting (or commenting) on them.
All that said, there are a few notable times in the story when the narrator’s own opinions emerge. Take the following passage, for example, when the narrator describes Félicité’s relationship with her long-lost sister Nastasie’s family:
Félicité became very attached to them. She bought them a blanket, some shirts and a cooking stove. They were obviously out to take advantage of her. Madame Aubain was annoyed that Félicité was not more firm with them.
The sentence “They were obviously out to take advantage of her” clearly does not come from Félicité here—the narrator has just described how Félicité “became very attached” to Nastasie’s family. In this moment, the narrator separates from Félicité and, using a frustrated and judgmental tone, expresses their personal distrust of Nastasie’s family. This is one of the few times in the story when the narrator’s perspective is closer to Madame Aubain’s than to Félicité’s (as Madame Aubain, too, is “annoyed” at the situation). This moment demonstrates how, despite having a compassionate orientation, the narrator is not necessarily as loving and trusting as Félicité, whose kindness seemingly knows no bounds.