What is the irony of the Quenu and Lisa attending a theater performance called "The Grace of God"?

Ironically, when the Quenus attend a performance at the Théatre de la Gâité, they see a melodrama entitled La Grâce de Dieu or "The Grace of God." The irony here is that La Belle Lisa does not believe in God per se, but only in her own good sense. La Belle Lisa is vindicated when she sees La Belle Normande and Mère Méhudin sitting in the upper balcony with the rest of the common people.