Justice is confusing, so resist the temptation to simplify.
In the first oration, "Pro Roscio Amerino," Cicero defends a client as his lawyer in the Roman court. That means that this speech was performed in front of the emperor and in front of the prosecution. His strategy in the case was to explain away the simplified accusation of patricide by explaining the context for his client's behavior, and by appealing to the personal justice of the jury—in this case, the emperor himself is the final authority.
It's easy to feel right, but it's difficult to communicate effectively.
An implicit theme that Cicero will sometimes comment on in the work is the difficulty of communication. Cicero was especially adept at finding nuance in an argument, and his first move in any disagreement is to call attention to the difficulty of justice and the complexity of the issue, so as to avoid oversimplification.
Another way this theme is addressed is in the concept of Status. Cicero says that people's words may sound the same, but often what they mean by those words is radically different. Cicero draws attention to the need for clear, complex communication that addresses the heart of a matter.
Humility and empathy are necessary components of ethical rhetoric.
If someone assumes that they are correct, then their rhetoric will fail to sound persuasive, because it won't contain the right amount of concession and reasonability. The solution to this problem is to find a way to practice open-mindedness, both because it will help shape your arguments, and also because after all, truth is so valuable that it's not worth feeling right while being wrong. The mark of rhetorical strength according to Cicero is the ability to entertain different points of view fairly.
Injustice can be solved through persuasive communication.
Although not in every case (certainly not in the final oration that ended with Cicero's own execution), many times brilliant rhetoric can serve the common good by moving authority figures against injustice. This is especially the case in In Catilinam where Cicero exposes the plot of Catiline to form a coup to overthrow the emperor.
