[…] a social life which seemed nothing but a labyrinth of petty courses, a walled-in maze of small paths that led no whither, the outcome was sure to strike others as at once exaggeration and inconsistency. (1.3.13)
This is an important passage for thinking about "dissatisfaction" as well as "society and class." Dorothea's dissatisfaction, after all, stems from her social position. She feels hemmed in and hampered by social expectations and conventions. The only options that are available to her seem "petty" and pointless.
But any one watching keenly the stealthy convergence of human lots, sees a slow preparation of effects from one life on another, which tells like a calculated irony on the indifference or the frozen stare with which we look at our unintroduced neighbour. Destiny stands by sarcastic with our dramatis personae folded in her hand. (1.11.2)
The narrator reflects on the development of important relationships between people: when you see someone for the first time, you have no idea whether they'll play an important role in your life, or not. You might feel "indifferen[t]" towards your "unintroduced neighbour" at first, only to find a few weeks or months or years down the line that they'll have a very important effect on your life. "Our dramatis personae" is the cast of characters in our own lives, which "Destiny" decides.
[…] a few personages or families that stood with rock firmness amid all this fluctuation, were slowly presenting new aspects in spite of solidity, and altering with the double change of self and beholder. Municipal town and rural parish gradually made fresh threads of connection. (1.11.3)
Even though many families in Middlemarch (like the Vincys, for example) have been there for ages and seem to be as "solid" as a "rock," they actually change over time, too. Just because you've known someone since childhood doesn't mean that they won't be capable of surprising you as an adult. The narrator also introduces the metaphor of the "threads of connection" between people – this is important for the "web" that gets woven throughout the novel. All of the characters in Middlemarch are connected to each other through these "threads of connection" that form a giant social "web."
Less superficial reasoners among them wished to know who his father and grandfather were, observing that five-and-twenty years ago nobody had ever heard of a Bulstrode in Middlemarch. (2.13.1)
Even though Mr. Bulstrode is a rich and powerful banker in Middlemarch, and therefore an important member of Middlemarch society, certain people still think of him as a newcomer. Unlike old Middlemarch families, like the Vincys, Bulstrode is an outsider even after twenty-five years. No one knows who his "father and grandfather were."
One can begin so many things with a new person! – even begin to be a better man. (2.13.4)
This passage points out the possibilities of forming new relationships: you can reinvent yourself when you meet new people, so you always have the potential to become "a better man."
I at least have so much to do in unraveling certain human lots, and seeing how they were woven and interwoven, that all the light I can command must be concentrated on this particular web, and not dispersed over that tempting range of relevancies called the universe. (2.15.1)
The narrator uses the metaphor of the social "web" again here – the "threads of connection" must be "unravel[ed]" to show "how they were woven and interwoven." This suggests that we're all related to everyone else in some complicated way. It's like "six degrees of separation."
Middlemarch, in fact, counted on swallowing Lydgate and assimilating him very comfortably. (2.15.26)
The town of Middlemarch is personified in this passage – the entire town is about to "swallow" Lydgate and "assimilate" him. Society seems like an ominous force of assimilation here – it's something that can consume you and take away your individuality and make you part of a whole, and Middlemarchers aren't always fond of thinking independently. So Lydgate's "assimilat[ion]" will take away his power to think for himself.
"It seems to me we know nothing of our neighbours, unless they are cottagers. One is constantly wondering what sort of lives other people lead, and how they take things." (4.34.12)
Dorothea reflects on how little people understand each other. People don't bother to try to stop and think about "what sort of lives other people lead, and how they take things." The exception, though, is the "cottagers." Is Dorothea saying that poor people are easier to understand that members of the wealthy upper class? Are they less complex as people? Or is she suggesting that members of the upper class are more concerned about hiding their true feelings because they have more to hide? It's not clear.