According to "The Edge of the Storm" by Agustin Yanez, how were the lower class and higher class affected by the Mexican Revolution?
Not only does Yáñez show the ideas about the Mexican Revolution through the eyes of characters in different classes, but he is also quite adept at portraying life in a Mexican small town as dull and drab and religious and even superstitious and condemning (especially about outsiders). In answer to your question specifically about the Mexican Revolution, we can use three characters as representations: Maria and Marta (as the representatives of the lower class) and Damián Limón (as the representative of the upper class).
I'll include just a tiny bit of Yáñez's background on the Mexican Revolution. Yáñez, of course, focuses on the revolution as brought about by both politics and social unrest. The Catholic Church was a big part of the social unrest (and corruption), and so there is a tendency for Yáñez to focus on the Church in the novel. In addition, the distribution of land and political reform are background causes.
Although there are other upper-class characters that can be used as representations (such as the distant dictator Porfirio Díaz), my choice is Damián Limón. Damián Limón was born into a wealthy family. He is young and the offspring of a prominent landowner in the community. Much to the chagrin of the superstitious community, Damián Limón leaves home in order to work in the United States. The community is unceasingly disgusted with Damián Limón upon his return. The reason why they are disgusted is as follows:
[The United States is a place] where Mexicans are treated like dogs.
Affected by this community, Damián Limón ends up murdering Micaela Rodríguez (he blames her for the death of his father), but is given such a light sentence because of his prominent wealth in the community. Damián Limón ends up joining the revolutionaries not only because he believes in the cause but also to escape the condemnation of the town.
Damián Limón aside, it's important to note that most of the characters in this novel are from the lower class and, as such, both Maria and Marta (orphans being raised by their uncle Don Dionisio) are good representations. Why? Because they are commoners who take different paths: one to the Revolution and one away from the revolution. Marta is fairly happy with her life in the town. She loves children, works at the hospital, and is a generally gentle and compassionate soul. Marta represents the best situation that results from the unrest of the Mexican Revolution. Maria is the opposite. Her eyes are always on rebellion. She is always reading banned books and speaking as the foil to Marta. Eventually, Maria leaves home to follow the army of the Mexican Revolution (because she can't join its ranks herself). She is a reaction to the peculiar environment of the town and its treatment of the lower classes.
In conclusion, it seems that fleeing from the judgmental towns to the army is the connecting factor for both upper and lower classes. Even though there is a large separation between upper and lower classes in Mexico at the beginning of the 1900s, both rich and poor flee their oppression in the same way: by joining the Revolutionaries in whatever way they can (such as Maria and Damián Limón). Those content to live within the oppressive small town (like Marta) remain and become examples of the best life the current Mexico can give.