A woman dictates before marriage in order that she may have an appetite for submission afterwards. (1.9.1)
The narrator makes this remark about marriage early on in the novel, shortly before Dorothea marries Mr. Casaubon. The comment is probably meant to be read ironically –do we really think that George Eliot believed that women should be "submissive" after marriage? Probably not. But that's the way society expected a wife to behave. So in this brief, almost throwaway remark, Eliot makes a huge, ironic commentary on the social expectations of wives.
all must admit that a man may be puffed and belauded, envied, ridiculed, counted upon as a tool and fallen in love with, or at least selected as a future husband, and yet remain virtually unknown – known merely as a cluster of signs for his neighbours' false suppositions. (2.15.1)
The narrator suggests here that Rosamond doesn't understand anything about her "future husband," Mr. Lydgate – but that her case is pretty ordinary. This is one of the many cases in which Eliot juxtaposes the particular with the universal. In other words, she takes Rosamond's specific experience (not understanding her future husband), and claims that it's a common enough case that "all must admit" it.
Poor Lydgate! or shall I say, Poor Rosamond! Each lived in a world of which the other knew nothing. (2.16.58)
This passage pretty much sums up the reasons why marriage fails in the world of Middlemarch (if not in the wider world): the two people don't understand each other at all. And the narrator tries to assure us that neither is to blame more than the other (she says both "Poor Lydgate" and "Poor Rosamond"). It's not a question of fault; it's just unfortunate – almost tragic.
In Rosamond's romance it was not necessary to imagine much about the inward life of the hero, or of his serious business in the world. (2.16.58)
Rosamond doesn't need to know anything about Lydgate's feelings, ambitions, or "inward life," because that's not part of the "romance" she has imagined for herself. Part of the reason her marriage is unhappy is because of the romances she has read. She tries to imagine herself as a romantic heroine, and Lydgate as a "hero," but of course that fantasy has nothing to do with the "serious business" of their lives.
She was as blind to his inward troubles as he to hers; she had not yet learned those hidden conflicts in her husband which claim our pity. She had not yet listened patiently to his heart-beats, but only felt that her own was beating violently. (2.20.25)
Dorothea is usually very sensitive and sympathetic to other characters, but she's not able to sympathize with her husband – she's not aware of his "inward troubles," and he's not aware of hers. And here's another instance of Eliot juxtaposing the particular with the universal. She says that Dorothea hasn't "learned" all of her husband's "hidden conflicts," which "claim our pity." By switching to the first person ("our"), instead of saying, "which would claim her pity," Eliot suggests that Dorothea's situation is a common, perhaps universal, one.
The duties of her married life, contemplated as so great beforehand, seemed to be shrinking with the furniture and the white vapour-walled landscape. (3.28.3)
Before her marriage, Dorothea had thought that the "duties of her married life" would be great and noble – she thought that her days would be filled with helping her husband with his book, and with pursuing knowledge that would somehow light up the world for her. In reality, though, her day-to-day life is filled with humdrum, mundane concerns, like dinner parties and social visits. The wide landscape that she had imagined has turned into a cramped sitting room filled with "furniture" and "white […] walls."
there was the stifling oppression of that gentlewoman's world, where everything was done for her and none asked for her aid – where the sense of connection with a manifold pregnant existence had to be kept up painfully as an inward vision, instead of coming from without in claims that would have shaped her energies. (3.28.4)
Part of Dorothea's dissatisfaction with her marriage comes from the fact that she has no work to do. She has so much energy and passion for doing good in the world that she's depressed to find that the cottagers and farmers at Lowick don't need her help. She has all this pent up energy and nothing to do. This was a problem for many upper class women in "that gentlewoman's world" – here's yet another case in which Eliot points out that Dorothea's individual case is part of a more common, universal trend.
but why always Dorothea? Was her point of view the only possible one with regard to this marriage? (3.29.1)
This passage reminds us that Dorothea's point of view isn't the only one. It's the narrator's way of reminding us what our grade school teachers used to drill into us: imagine what it's like to be in the other guy's shoes. Since this novel is all about sympathy, it's important to remember that Mr. Casaubon has his own perspective on what's going on, too – and we have to imagine what it's like from his point of view.
Marriage, like religion and erudition, nay, like authorship itself, was fated to become an outward requirement. (3.29.4)
Part of why Casaubon is so unhappy is that he's not passionate about anything. He's very wrapped up in doing the right thing, but doesn't care deeply about any of his work anymore. His religion, his scholarship, and the book he's writing are all just things that other people expect of him, not things that he's passionate about. And the saddest part is that his marriage is rapidly falling into the same category.
Lydgate thought that after all his wild mistakes and absurd credulity, he had found perfect womanhood – felt as if already breathed upon by exquisite wedded affection such as would be bestowed by an accomplished creature who venerated his high musings and momentous labours and would never interfere with them; who would create order in the home and accounts with still magic, yet keep her fingers ready to touch the lute and transform life into romance at any moment; who was instructed to the true womanly limit and not a hair's-breadth beyond – docile, therefore, and ready to carry out behests which came from beyond that limit. (4.36.71)
This passage shows just how delusional Lydgate is when he's contemplating his future wedded bliss with Rosamond – he idealizes her, and thinks only about how she'll make his life perfect, without considering the whole thing from her point of view. Like Rosamond, Lydgate's fantasy is inspired by the romances he's read. He expects Rosamond to be like an ideal fairy princess, who will somehow transform the mundane and everyday "home and accounts" into fairy land through her "romance" and "still magic." Notice, though, that his fantasy doesn't include Rosamond's having a personality or desires of her own beyond making his life easier.
Lydgate relied much on the psychological difference between what for the sake of variety I will call goose and gander: especially on the innate submissiveness of the goose as beautifully corresponding to the strength of the gander. (4.36.100)
Lydgate's fantasy is based partly on romance, but also partly on his observations in the natural world – on the natural difference in strength between male and female. He assumes (incorrectly) that since females are less strong than males, they are therefore proportionally more docile and submissive. That's just bad science, right there.
However slight the terrestrial intercourse between Dante and Beatrice or Petrarch and Laura, time changes the proportion of things, and in later days it is preferable to have fewer sonnets and more conversation. (4.37.18)
Here's another place where the narrator jumps from the particular experiences of her characters to universal statements about everyone who lives "in later days." In this case, she alludes to two famous poets: Dante and Petrarch. Both of these Italian poets were famous for writing love poetry to idealized, distant women (named Beatrice and Laura, obviously). Both poets express their despair of ever being with the woman in question, and both poets set the object of their affection on a pedestal and make her seem like she's something more than human. This passage comes in a chapter in which Will Ladislaw is despairing of ever seeing Dorothea again. The narrator says that distant, idealized love is all very well in poetry, but that "in later days" it's more important to a relationship to have rational "conversation" than sonnets.
"Marriage is so unlike everything else. There is something even awful in the nearness it brings." (8.81.25)
This is one of the last general remarks about marriage in the novel. Dorothea is talking to Rosamond and advising her to take care of her marriage to Lydgate because there's no getting out of it. This particular remark is about how scary intimacy can be – when she says "awful," of course, she doesn't mean "horrible," but rather "awe-inspiring" or "almost scary."