"A Simple Heart" marks a significant transformation in Flaubert's work. It is a narrative of redemption, something exhibited in the use of the term "simple." When his good friend, George Sand, encouraged Flaubert to compose literature that represented narratives of "consolation, rather than desolation," the idea of human consciousness as being "simple" becomes a part of this construction.
The idea of a "simple" heart for Felicite is reflective of the selflessness Flaubert constructs as part of her being. Felicite is of a "simple" heart. She is able to subjugate her own sense of identity into something larger. Consider how different this is from another one of Flaubert's constructions, Emma Bovary. Emma is far from "simple" as her mind is constantly embroiled in machinations and manipulations. Emma is more concerned with everything that is far removed from simplicity and being "simple." In this, one can see how and why Emma dies the way she does, without consolation and filled with desolation. Flaubert sees in Emma's complexity a desire for the garden, only to wind up in a desert.
For Flaubert, Felicite's "simple heart" is a blueprint in how to find happiness in the modern setting. Felicite's "simplicity" lies in her innocence. She is incapable of acting in a malevolent or duplicitous manner. She sees only the potential for good. In this light, she finds peace in her being. Those who are fortunate enough to be around her also find this same peace, such as Virginie and Madame Aubain. The use of "simple" is to describe a person without devious intent, devoid of machinations and being driven by the desire to manipulate. Felicite's happiness is found in the selflessness and altruism she displays. In a world of desolation, where human capacity and ingenuity is often used for the very worst of ends, Felicite represents this "simple nature. In this capacity, Flaubert uses "simple" to convey the hope for redemption and consolation.