Societal instability
The core theme that ties the novel together is the theme of societal instability, which comes in several forms. First, there is the war in Europe, and unlike Americans of this time, many French Canadians in this novel still feel attached to their European homelands, so this war represents a serious threat to society. Then there is the economic instability of the oppression of the working class. That is an undeniable part of the book, especially given the drama between young Florentine and her boyfriend, Jean. When Jean finds out that Florentine is secretly poor, he has sex with her and then leaves. Not just the house, either—he leaves town, never to be heard from again. This is a picture of social division due to economic class.
Poverty and judgment
This novel addresses the way poverty is perceived by others. This is most obvious when Jean leaves Florentine for being too poor for his taste, but there are more subtleties in the novel that indicate the same idea. Part of what makes Emmanuel a good option in the end is that he doesn't care about Florentine's station in life, because he knows he can take care of her. Then there are the subtleties of Jean's character, for example, he is planning to get very rich by exploiting the need for machinery because of the war. He is set up to profit from the economic instability of his community, which might help explain his aversion to poor people.
Sickness and happiness
Instead of using sickness to symbolize decay and death, this novel uses Daniel's leukemia as an opportunity to explore ways in which Daniel's sickness might be his greatest blessing; having been raised in absolute poverty, he often finds himself extremely happy at the hospital, because the amenities and environment are that much better than what Rose-Anna is able to provide him at home (by absolutely no fault of her own).
