The theme in Chains is that you have to fight for what you believe in no matter what the consequences are. An example I the story is when Isabel learns that Ruth was sold, she didn't pretend like nothing happened, she actually confronted Madame.
Another example in the story is when Isabel learns that Madame's husband is planning against General George Washington. Isabel sneaks out during the night to tell the resistance against King George that Madame's husband is planning to assassinate Washington. If she were to be caught sneaking out at night she would probably be executed because she is a slave.
If I were in Isabel's position I don't know if I would really risk my life to warn a couple of rebels. This is why I believe that the theme in Chains is to never give up. Isabel show tremendous amounts of courage throughout the story and by doing so creates a lesson that cannot be forgotten.
-By Noah ノア