About this passageThe opening chapter of the handbook, and the division everything else in it rests on. Epictetus sorts the whole of experience into two piles and puts body, property and reputation firmly in the second. The final paragraph gives the practical drill: meet each impression as it arrives, test which pile it belongs to, and if it belongs to the second, say so.
There are things which are within our power, and there are things which are beyond our power. Within our power are opinion, aim, desire, aversion, and, in one word, whatever affairs are our own. Beyond our power are body, property, reputation, office, and, in one word, whatever are not properly our own affairs.
Aiming, therefore, at such great things, remember that you must not allow yourself any inclination, however slight, toward the attainment of the others; but that you must entirely quit some of them, and for the present postpone the rest.
Seek at once, therefore, to be able to say to every unpleasing semblance, "You are but a semblance and by no means the real thing." And then examine it by those rules which you have; and first and chiefly by this: whether it concerns the things which are within our own power or those which are not; and if it concerns anything beyond our power, be prepared to say that it is nothing to you.
In plainer words
Some things are up to you and some are not. Up to you: what you think, what you aim at, what you want, what you avoid — your own choices. Not up to you: your body, your possessions, your reputation, your job. Since what you are after is that big, do not let yourself get pulled even slightly towards the other things; drop some of them entirely and put the rest off for now. When something unpleasant turns up in your head, get in the habit of saying "you are just an impression, not the thing itself" — then check it: is this in my control or not? If it is not, tell yourself it is nothing to you.
A restatement in modern English, written for this collection. The passage above is the text; this is one way of putting it.