What are the motifs in Catherine, Called Birdy by Karen Cushman?

The importance of maintaining the social hierarchy is evident in almost every aspect of Catherine, Called Birdy. The most important example of this is Catherine's pending marriage. In the first place, she has to marry somebody of her station in life or higher in order to please her father and maintain her position in society. Thus, the men (old and young) who come into her life as potential suitors all represent ways of keeping this position, which she does not care about.