Find the central sentence of the selected paragraph. Tell me your understanding of this sentence (please see the supplementary question)

This is public morality, this is the rule! This sentence is the central sentence.

This sentence explains why Big Brother Black not only returned the watch to the author, but also reported the author. Everything is because of public morality and rules. The so-called public morality is the code of conduct for what we should and should not do for the benefit of the group. A person who doesn't abide by public morality is bound to be discriminated against by everyone. When he came to this world, he must abide by public morality and rules.