I don't think there is a moral to Black Beauty but the author advocates for fairer treatment of horses in Victorian England.
The story is narrated from Black Beauty's perspective and possibly readers gained insight into how horses suffered through their use by human beings with restrictive technical objects like the "bearing rein" and "blinkers" as well as procedures like cutting off the tails of the horses.
The moral lesson of it is not to be envy..
Moral lesson in karaniwang tao
moral lesson of dahong palay
moral lesson of the commedy of errors
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moral lesson in mill on the floss
Elephant and Friends moral lesson
The lesson in a story is called the moral.
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moral lesson of being care giver