About this passageThe closing part of a longer entry that begins by observing that people seek retreats — houses in the country, seashores, mountains — when the only retreat always available is inward. What follows is the summary Marcus gives himself: two things to keep at hand, and a definition of what disturbance is made of. The last sentence is among the most quoted in the book.
This then remains: Remember to retire into this little territory of thy own, and above all do not distract or strain thyself, but be free, and look at things as a man, as a human being, as a citizen, as a mortal.
But among the things readiest to thy hand to which thou shalt turn, let there be these, which are two. One is that things do not touch the soul, for they are external and remain immovable; but our perturbations come only from the opinion which is within.
The other is that all these things, which thou seest, change immediately and will no longer be; and constantly bear in mind how many of these changes thou hast already witnessed. The universe is transformation: life is opinion.
In plainer words
So: remember you can withdraw into that small patch of ground that is your own. Do not wind yourself up. Be free. Look at things as a person, a human being, a citizen, someone who will die. Keep two things where you can reach them. First, events do not touch your mind — they are outside it and they stay outside; the disturbance is the opinion you are holding. Second, everything you can see is already changing and will shortly not be there, and you have watched that happen more times than you can count. Everything is turning into something else. Living is a matter of what you make of it.
A restatement in modern English, written for this collection. The passage above is the text; this is one way of putting it.