What are the themes in Conscience of the Rich?
I would say a theme prevalent throughout the novel is the theme of religion. The March family is a Jewish family and Leonard is adamant that his family stay Jewish. He is pleased, to a certain extent, that Charles is going to marry Ann (a Jewish girl). He is upset that his daughter, Katherine, is in love with Francis (a gentile).
A second theme is the bonds of family. Leonard is the strong and demanding head of the March household. It's a wealthy family too, and Leonard frequently uses money to control what his sons and daughters do. Despite that overbearing attitude, Leonard loves his children and wants to them be successful. Katherine and Charles both do things (marriage and career changes) that upset Leonard, but neither person takes those decisions lightly. They know how it will affect the family.
Another theme is the theme of wealth and power. I mentioned a bit about it in the previous paragraph. The March family is very wealthy. Leonard uses that wealth to control his family. There are several times that Leonard threatens to take away Charles's financial independence or monthly allowance. That threat actually makes Charles toe the line for quite some time. Being wealthy like that gives Leonard a bloated sense of power.
Revenge is present in the novel. Porson is bent on seeking revenge against multiple characters for a variety of reasons.
There is the theme of political affiliations in the novel with Ann working for a Communist newspaper.
I'm sure you could list love as a theme as well. You've got characters that fall in love and marry outside of the faith and/or against parents' wishes.