On the order of Seneca’s Letters to Lucilius (and 6 Stoic Rules for Life)

Unlike today, philosophers like Seneca used to philosophise in letters (image unsplash)

Why did Seneca write his Letters to Lucilius, in which he expounds his philosophy, and what ordering (if any) can we find between them? Or, is there no such order, so each letter can be taken (and left) on its own?

According to Ilsetraut Hadot in her yet-to-be-translated book Sénèque, there is an order and a method in the “chronological…