How we cite our quotes:
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.