If you wish to have peace and contentment, release your attachment to all things outside your control.

Epictetus is reminding you that serenity and stability are results of your choices and judgment, not your environment.

Remove your aversion, then, from everything that is not within our power, and transfer it to what is contrary to nature among those things that are within our power. For the present, however, suppress your desires entirely; for if you desire any of the things that are not within our power, you’re bound to be unfortunate, while those that are within