Hadot notes that metamorphosis or change is a recurring idea in the book (The Inner Citadel, p. 270):
In Book VIII, the theme of universal metamorphosis takes on a very particular form. Here, Nature has the power to use the detritus which results from its vital activity to create new beings (VIII, 50). Since it has no space outside itself where it can throw this detritus, it transforms it within itself and makes it into its matter once again (VIII, 18). Intellectual or rational nature, for its part, transforms the obstacles that oppose its activity into a subject for exercises, which thereby permits it to attain its goal by using that which resists it (VIII, 7, 2; VIII, 32; VIII, 35; VIII, 41; VIII, 47; VIII, 54; VIII, 57).
On the basis of this universal changefulness, we should not be afraid of new things (VIII, 6); all things come and go on the basis of a law that is like divine law, so that even death is ordered (2, cp. 17). That a thing cease belongs as much to its nature as that it be born or continue to exist (20). When we deal with the world, we should deal with it as it really is, and one of the questions we should ask is how long it lasts (11). Even things we do not like -- bitterness in cucumbers and thorny bushes, for instance -- each comes and goes and becomes a way for new things to arise according to the order of the universe (50).
For our part, it is in our power to change ourselves or keep to our straight course (16). If things are in our power, we cannot blame either atoms or the gods, the only other causes involved; we either set ourselves right or set the situation right, and if we can do neither, it is absurd to complain (17). Since in this changeful universe, everything comes to be from a purpose, we should ask ourselves what the purpose of our coming to be was, and recognize that it could not possibly be pleasure (19). We can form a better picture by considering our natures:
A man's joy is to do what is specifically human, and it is specifically human to be gracious to his kind, to despise the activities of the senses, to judge aright the persuasive pictures of the imagination, to contemplate the nature of the Whole and all that happens in accord with it. (26)
In a rational creature we can see that there is a virtue that opposes pursuit of pleasure (39).
Two other choice comments:
"Accept without conceit, relinquish without reluctance." (33)
"Men are born for each other's sake. So either teach people or endure them." (59)
One of the features of the ninth book is that, interspersed among its short reflections, it has several extended meditations (these longer meditations tend to come more thickly in the last few books of the work). It's worthwhile to get some sense of the basic idea of some of these.
At IX,1, we get a discussion of impiety. Injustice is impious because the Whole has made rational creatures for each other; wrongdoing is a transgression against the Whole as the oldest goddess. Lying is also impious, for the Whole is Truth herself, "the first cause of all that is true." There is a double wrongness here, since the liar wrongs others and is out of harmony with the Whole. Living one's life in pursuit of pleasure as good and in flight from pain as evil is also impious, because the Whole distributes pleasure and pain in accordance with the good of the Whole.
At IX, 3, the Emperor reflects on death. Death is one of the things intended by Nature, just as every other stage of life is, so we should not despise it, or regard it with exaggeration or arrogance. AS a way of encouraging himself to do this, he notes that death will not part him from people who have similar views from himself; at court he lives out of tune with everyone around himself.
At IX, 9, we find a discussion of community. Everything seeks its like, and this includes those things that are similar in having an intelligent nature. Even animals form communities of a sort, having "an increasing tendency to unity which does not exist in plants or stones or timber." Human beings, rational animals, have an even higher tendency to union; higher beings like the stars are even more united, so that "a rise in the scale of beings brings a common feeling even among those who are far apart." But intelligent beings can also forget that they have this urge -- they cannot get rid of it, because it still motivates them, but they resist it or even flee from it.
IX, 40 discusses prayer. If the gods have no power, it makes no sense to pray to them. If they do, why would we spend our praying on trivial things rather than asking for things like the ability to rise above our passions. If gods cooperate with human beings, they would surely do so by aiding us in this way. If, however, you were to say that these things are in our own power, then we should recognize it is just as absurd to spend our own power on the same trivial things rather than on rising above our passions; but in fact, on what ground would we conclude that the gods cannot help us even in matters in our power? "At any rate, start praying for these things, and you will see." Instead of praying for trivial or immoral things, pray for help in being moral, and see what happens. (We might call this Marcus Aurelius's Wager!)
IX, 42, the closing meditation in Book IX, concerns dealing with other people. If someone offends you through being shameless, ask yourself if there could be no shameless people at all; since there can't, you should stop demanding the impossible, because that is truly shameless. And similar arguments can be used across the board, for every kind of wrong. It is also good to develop the habit of asking, as a first reaction, what quality nature has given us to deal with this problem. If someone is offensively headstrong, for instance, we should consider that nature has given us gentleness for dealing with such people. Further, you should reflect that you have not really been injured, if you yourself do not use the occasion for becoming worse. Further, if it happens that you already knew that he was foolish, why did you expect him not to act foolishly? But most importantly, when you encounter these vices, you should take the opportunity to reflect on yourself, and what wrong you might have done -- perhaps you were imprudent in trusting the disloyal man, or did not benefit someone because it was a good thing to do, but only because you were trying to trade it for some trivial thing.
Other comments of note:
"The sinner sins against himself; the wrongdoer wrongs himself by making himself evil." (4)
"One may often do wrong by omitting to do something, not only by doing something." (5)
"Today I left the troubles surrounding me, or rather, I cast them out. For they were not outside but within me, in my assumptions." (13)
"The wrong done by another you must leave with him." (20)
Hadot notes (The Inner Citadel, p. 297) that there is a recurrent theme of seeing people realistically in this book. In addition, we get something of an emphasis on simplicity and goodness. It opens with Marcus interrogating himself about when he will become simple and good (IX, 1), an interrogation that is repeated later in different terms (9). In an extended meditation, he recommends to himself that he focus on the few key virtues, and that if he begins to lose them he should either retire into seclusion to focus on them or depart life in simplicity rather than anger (8). Since time is short, we should live as if we were on a mountain (15). We should see to it that nobody can say anything of us except that we are simple and good (32).
to be continued