On the Happy Life, Section 4 — In Plain English

Seneca — The Senator

A person who lives by these principles will naturally have steady happiness and deep joy. This joy comes from above because he delights in what he already has. He doesn't need any pleasures beyond what his own life provides. Isn't he wise to let these inner pleasures outweigh the petty, silly, and brief complaints of his weak body? The day he becomes immune to pleasure, he also becomes immune to pain. Look at the opposite — how evil and guilty is the slavery of someone who is ruled by pleasures and pains. These are the most unreliable and demanding masters you could have.

Seneca — The Senator Original

A man of these principles, whether he will or no, must be accompanied by a continual cheerfulness, a high happiness, which comes indeed from on high because he delights in what he has, and desires no greater pleasures than those which his home affords. Is he not right in allowing these to turn the scale against petty, ridiculous, and shortlived movements of his wretched body? on the day on which he becomes proof against pleasure he also becomes proof against pain. See, on the other hand, how evil and guilty a slavery the man is forced to serve who is dominated in turn by pleasures and pains, those most untrustworthy and passionate of masters.