It is a sort book but it is interesting. You have an introduction about Seneca’s life before going through the letters. I liked as it gives some background about the person. As well, I didnt remember/know he was Nero‘s teacher and advisor.
It seems the letter were written during his exile and they cover a lot of aspects of his life and Stoic philosophy. It covers topics like poverty and richness from a Stoic point of view, keeping in mind that he was a rich man can be a bit surprising but it takes his wealth the Stoic way, if it goes, he will be fine. As well, touches a very interesting subject like slavery, that was the base of all Rome economy. He states everybody is a slave of something. The “free” romans were slave of vices: power, money, etc. And clearly says you need to treat a slave like you want to be treated, so it looks like it reduces the slavery to a concept of labor contract, and I think there is touch of “Christianity” in some comments. He was contemporary of Jesus. Maybe a coincidence.
He writes about many subjects like how you need to speak slowly, only mourn/cry the minimum time (very stoic), suicide vs illness (stoic), not taking hot baths, Scipio of Africa, olive trees, Socrates, vegetarianism, excess of alcohol, Socrates, Pythagoras, dont have a night life, negative of having bad companies, etc.
So I liked it, it wasn’t a hardcore book about philosophy so you read it like the memories of an interesting person in history.