After the assassination Julius Caesar, Cicero wrote “On Obligations” to his son Marcus, who was studying in Athens. He obviously meant it for the public as well, but it has the sense of a father writing to a son.
It might be the most important book on ethics in the West, at least until recent years. Yet it’s recent decline in popularity does not gainsay its classic status or the reason why it become a classic—classics become so because they have a sense of excellence.