How we cite our quotes: (Book.Chapter)
Quote #1
Now every part of nature benefits from that which is brought by the nature of the Whole and all which preserves that nature: and the order of the universe is preserved equally by the changes in the elements and the changes in their compounds. Let this be enough for you, and your constant doctrine. (2.3)
Marcus tells us that the universe is controlled by two conflicting principles: change and order. In this case, the structure and preservation of the universe is dependent on the change that constantly reshuffles the distribution of substance. While the maturing and decay of human life is exactly the thing that turns Marcus off to a life in the body, it's also the thing that keeps the universe ever new: the recycling of elements makes it possible for new things to be born all the time.
Quote #2
In man's life his time is a mere instant, his existence a flux, his perception fogged, his whole bodily composition rotting, his mind a whirligig, his fortune unpredictable, his fame unclear. To put it shortly: all things of the body stream away like a river, all things of the mind are dreams and delusion; life is warfare, and a visit in a strange land; the only lasting fame is oblivion. (2.17.1)
Here's your cheerful thought for the day: humans are rotting, inconstant heaps o' atoms. Marcus strings together a line of metaphors to make sure we understand the transient nature of human existence. Of special interest here is the comparison of human on earth to strangers in a strange, hostile land. Though Marcus does not speak of an afterlife in detailed terms, this phrase hints that he imagines his true home to be elsewhere—perhaps as part of the universal Whole. Though the universe itself is a place of constant change, there's an inevitability and purpose to such transformation. On earth, change means brevity and decay.
Quote #3
... all these things you see will change almost as you look at them, and then will be no more. Constantly bring to mind all that you yourself have already seen changed. The universe is change: life is judgement. (4.3.4)
Marcus often uses the metaphor of existence as a river to convey how quickly individual people and other living things are swept through life and disappear. The speed of this turnover convinces him not to value anything that lives on earth, since all earthly life is so impermanent. There is no bitterness in his observations: life is change, he says, so get used to it.