The main theme of Black Beauty is the care of animals, particularly horses. Many people have said that Sewell could have written a non-fiction text describing the care of horses instead of Black Beauty because there is so much in it on how to care for them. In this care, Sewell also alerts the reader to the abuse of animals. The reader wanted to gain sympathy from her readers for these animals in an attempt to help end the abuses.
One other theme would be morality and righteousness. Sewell was raised as a Quaker and therefore had a strict personal code of conduct. This strict behavior is seen throughout the work.