| Quote #1
Férula […] reminded him that on their mother's side they were heir to the noblest and most highborn surname of the viceroyalty of Lima. Trueba had simply been a regrettable accident in the life of Doña Ester, who was destined to marry someone of her own class, but she had fallen hopelessly in love with that good-for-nothing immigrant, a first-generation settler who within a few short years had squandered first her dowry and then her inheritance. (2.21)
In Férula and Esteban's pride in their mother's surname, we get the sense that "class" is a category separate from wealth – nobility can't be lost just because a family loses its money. Class is a more enduring label, which suggests that, in this society, members of the lower class couldn't easily shed the stigma of their low birth by making a fortune.
| Quote #2
The upper class, however, in whose hands were concentrated all the power and wealth, was unaware of the danger that threatened the fragile equilibrium of their position. (2.72)
Though class is regarded by many characters in the novel as a stable and immutable category, the author hints that the category is more "fragile" than they suppose.
| Quote #3
Word of his cruelty spread throughout the region, provoking jealous admiration among the men of his class. They peasants hid their daughters and clenched their fists helplessly because they could not confront him. Esteban Trueba was stronger, and he had impunity. (2.74)
Upper-class status comes with a get-out-of-jail-free card. Esteban Trueba can do whatever he wants with impunity.