A purposeless life is a wasted life
Egon von Ernau begins the novel as a young nobleman who, having lived only for himself, feels as though life has nothing more to offer him. Although he has been able to gratify every material, intellectual, and aesthetic desire, he feels as though his life is purposeless. Only when he meets the von Osternau family and their acquaintances and retainers does Egon finally realize that a life with purpose and structure is deeply satisfying. The characters who do not embrace a higher purpose, and who seek only their personal gratification, may attain material reward but they never become happy.
Duty
Throughout the novel various characters find themselves in conflict between different kinds of duty. Bertha von Massenburg and Albrecht von Osternau believe that people of rank have a duty to their own class and to their family's heritage, and that this duty takes precedence over things like a desire for personal happiness. The characters who are derelict in their duty, such as the weak and ineffectual Gottlieb Pigglewitch, seldom accomplish much.
The danger of gambling
The quicksands in the title of the book-- note that no quicksand whatsoever appears in the novel-- represent the danger of habitual gambling. Pigglewitch ruins himself financially three times and finally commits suicide after he has gambled away his patrimony, a windfall from Egon, and additional money from Egon intended to help him start anew. Albrecht loses his cavalry commission, his honor (he becomes a thief and attempts to frame "Pigglewitch" when Albrecht steals the money the Baron von Osternau has set aside for Lieschen), and eventually his family due to his attempts to pay off gambling debts.
Rank and good character are separate things
Simply being from a noble family does not, by itself, guarantee a good reputation. Bertha's father, the Baron von Massenburg, attempts to effectively sell his daughter to the von Ernau family in exchange for cancellation of his debts. Albrecht becomes a thief and an arsonist, and Egon's father is a self-absorbed egotist. Until Egon stops behaving like a spoiled brat, takes responsibility for his own behavior and its consequences, and learns to control his impulsive behavior and to act with due regard for others, his reputation is just as bad as his father's. There are good examples of aristocrats also, such as the von Wangen family, so the author is not trying to imply that there's something wrong with the idea of social hierarchy. He does, however, show that good character and bad character are not confined to any particular social class. Albrecht and Pigglewitch, for example, are both compulsive gamblers who ruin themselves.
Pretense
Many characters in the novel masquerade as something they are not. Egon, a wealthy young nobleman, masquerades as the tutor Pigglewitch. Bertha, a gold-digging schemer, passes herself off as a sweet and innocent young lady with perhaps a little too much filial loyalty. Albrecht pretends to be a loyal family member when in reality he despises his cousin the Baron and steals from him at every opportunity.
Rank
Much of the novel focuses on the behaviors appropriate to the hereditary elite: the noble families that are frequently wealthy and politically influential. Emma von Osternau and her husband the Baron consider themselves to be quite liberal and willing to socialize with any reasonably well educated person regardless of rank, however everything the von Osternau family does is characteristic of the wealthy rural elite. The gestures, greetings, and protocols of the upper class appear throughout the book: the depth of a bow has significance, as does the behavior of a man when entering a room where members of the titled nobility are present. Exactly what is, or is not, appropriate to a person from a noble family is vigorously debated throughout the novel.
