Quakers as a symbol
This story swept through America at lightning speed. It captured the zeitgeist, which means it captured the cultural nuances of its time, and it touched on something that many people felt but few were capable of arguing so thoroughly as The Quaker City does. Quakers are a symbol in the book for religion, and the community is shown to represent the frustrating duplicity of appearance-oriented justice.
The trials as a sign
There is a famous motif from very early in human history (far older than written word in fact) of scales as a sign of justice. In this novel, the two trials serve as a kind of scale, evaluating justice as it pertains to money and appearance. What the novel discovers through its plot is that although everyone in the community enjoys the feelings of injustice and scandal, the community is mostly interested in preserving the status quo. The powerful aren't held to the same justice.
The boat passage
Here is a macabre idea: perhaps the final boat passage is a symbol for death. The storms of the open sea are far different than the daily troubles of life in community. The idea of the novel ending with a passage over waters is very reminiscent of a popular death motif (like crossing the river Styx in Greek literature, or the Jordan River in the Bible—Egyptian and Hindu mythology as well). This symbol could be for juxtaposition, to clarify how absurd this human experiment of justice really is, and what the stakes are.
Lawyers and legalism
There is a difficult lesson to try and grapple with presented in the story. The law is applicable and helpful, and yet, by attaining seats of power, incomplete people are able to exploit the law for its ability to see justice done a certain way. Lawyers are people who are skilled in legal combat, so they serve in the novel as a symbol for the various uses of law, besides the intended theoretical purpose of keeping people safe from violence.
The two murders
The actual content of the cases are two murders committed by different men. The first is acquitted because he is rich, but he straight up murdered his own wife in cold blood for betraying him. Is justice done for that frustrated wife, who survived in what the reader could easily guess was an abusive marriage? She finally finds someone who will treat her like a human, and he kills her for it. Then, there is the man who kills a real rapist. That man is judged. The only difference really is that in one case, a man is murdered, and in the other a woman is murdered. It is a clue about misogyny.
