Rich versus Poor
The Republic is a place of extreme economic polarization. High-ranking characters like June and Thomas enjoy lavish lifestyles and fancy events, while the poor live in slums and don't receive adequate medical care. Just as importantly, the Republic limits the opportunities that poor people have to succeed. Lu suggests that scores on the Trial are determined by how much money a person has, a system that helps the rich get richer and the poor stay poorer. Ultimately, the terrible conditions in the Lake sector help convince June to question the Republic and its values.
The Law
From the beginning of Legend, Marie Lu encourages readers to think about when it is right to follow the law and when it's not. She suggests that just because something is the law doesn't mean that it's right. Through Day's charitable crimes, she also suggests that sometimes good citizens need to break the law if their government is corrupt. On the other hand, people who choose to break the law need to consider the consequences of doing so. Although Day seems to believe his crimes are worth the punishment, understanding and accepting in advance what will happen to him if he's caught helps him behave with dignity under pressure.
Rebellion against Authority
Day and June rebel against the Republic in very dramatic ways. However, Legend also features average people engaging in small acts of rebellion as part of everyday life. Examples of this include the man who shelters Day and Tess after the hospital raid, the people who boo at Day's sentencing, and the old quarter that Day's parents safeguard as best they can. Because Day and June are exceptionally intelligent, they are able to rebel in more spectacular ways than average citizens like Day's family. However, Lu suggests that in a corrupt society, both types of rebellion are courageous and productive.
Family
All of the protagonists in Legend are primarily driven by love for their families. This love takes many different forms, positive and negative. After Metias dies, June has no family, so she instead focuses on getting revenge for his murder. Day, on the other hand, stays in Los Angeles despite the danger and the miserable conditions so he can continue to provide for his mother and brothers. Lu also acknowledges the importance of adopted families. Tess becomes as important to Day as a blood sibling; at the end of the novel, he decides to check on her even before rescuing Eden. Similarly, Lu hints that by the end of the novel, June has begun to see Tess and Day as her family. This interpretation of their relationship helps explain why their friendship allows June to finally let go of her anger about Metias's death.
Observation
One of the main ways that Day and June demonstrate their intelligence is through their incredible powers of perception. This common ability shows that the characters are intellectually curious, and in some sense kindred spirits. Lu also suggests that there's a connection between good observation skills and critical thinking. Thomas, who never questions his government, rarely pays attention to his surroundings, whereas the more critical characters are all depicted as more observant.
Perfection
Throughout Legend, Lu toys with the concept of perfection. Day and June both got perfect scores on their Trial. But are they perfect people? Day is described as so physically perfect that the Republic wants to use his DNA to make contact lenses. However, both characters have flaws. June is naive about her government and turns a blind eye to its cruelties. Day can be self-centered and sometimes has trouble empathizing with others. The author suggests that even people and things that seem perfect always have flaws if one looks carefully enough.
Violence
In Legend, characters' attitudes toward violence often hint at their overall morality. Despite their jobs in the military police, June and Metias are both uncomfortable with hurting people. Likewise, Day refuses to kill anyone and regrets even small acts of violence. On the other hand, Thomas unflinchingly orders soldiers to kill 100 protesters, and he even murders his best friend when ordered to by his superiors. In a society where morality is often murky, a character's relationship with violence signals who is good and who is bad. However, there is a degree of complexity to Lu's depiction of violence. Despite his discomfort with hurting others, Day seems to have no problem betting on Skiz fights. Kaede is also an example of a character that is (presumably) good but doesn't mind violence.
