Letters 75.18

There await us, if ever we escape from these low dregs to that sublime and lofty height, peace of mind and, when all error has been driven out, perfect liberty. You ask what this freedom is? It means not fearing either men or gods; it means not craving wickedness or excess; it incans possessing supreme power over oneself. And it is a priceless good to be master of oneself. Farewell.

Seneca, Letters to Lucilius 75.18, translated by Richard Mott Gummere