That the man and woman were husband and wife, and the parents of the girl in arms, there could be little doubt. No other than such relationship would have accounted for the atmosphere of domesticity which the trio carried along with them like a nimbus as they moved down the road. (1.4)
This is the opening image of the novel: a man and woman walking down a road together, a child in the woman's arms. No one speaks. The man seems contemptuously indifferent to the wife and child. And yet, the narrator assures us that it's obvious that the two are married, because a marriage brings with it a kind of "nimbus" of "domesticity" that any outside person can detect. Why should marriage bring with it a "nimbus" (a cloud)? Sounds pretty ominous.
The ruin of good men by bad wives, and, more particularly, the frustration of many a promising youth's high aims and hopes, and the extinction of his energies, by an early imprudent marriage, was the theme. (1.25)
The man (who still hasn't been named yet) keeps harping, in public and in front of his wife, about what a pain marriage is. He makes generalizations about how wives ruin their husbands. We don't directly hear what the man is saying; the narrator describes it in general terms. This could have the effect of making the man's complaints seem more reasonable, or at least fairly commonplace.
For my part I don't see why men who have got wives, and don't want 'em, shouldn't get rid of 'em as these gipsy fellows do their old horses. (1.30)
The man takes things a little far when he makes a comparison between wives and "old horses."
"Will anybody buy her?" said the man. "I wish somebody would," said she firmly. "Her present owner is not at all to her liking." (1.43-44)
From the beginning of the auction scene, it's clear that Susan thinks of her husband as a "master" in an economic sense, as well as a legal and moral one – she refers to him, with possible irony, as her "present owner".
Seizing the sailor's arm with her right hand, and mounting the little girl on her left, she went out of the tent, sobbing bitterly, and apparently without a thought that she was not strictly bound to go with the man who had paid for her. (1.80)
Susan's innocence is important: she doesn't realize that the "wife sale" that just took place isn't legally binding. After all, you couldn't just buy and sell people like slaves in 19th century England. But Susan doesn't understand this. If she did, her departure with the sailor would be like running away with someone to commit adultery. Since Susan thinks the marriage has been legally and morally transferred, she is innocent of any intentional wrongdoing.
The sailor was now lost to them; and Susan's staunch, religious adherence to him as her husband, till her views had been disturbed by enlightenment, was demanded no more. (4.9)
We're never told that Susan loves the sailor, but she thinks it's her duty to stay with him "as her husband."
In 1705, a woman who had murdered her husband was half-strangled and then burnt there in the presence of ten thousand spectators. Tradition reports that at a certain stage of the burning her heart burst and leapt out of her body to the terror of them all. (11.5)
This is an odd and gory detail for the author to include in the description of the history of the Casterbridge Ring (the old Roman amphitheater). It's about a woman's sins being publicly punished, and the almost supernatural way her remorse and sorrow are shown to the world (her "heart burst").
He pressed on the preparations for his union, or rather re-union, with this pale creature in a dogged unflinching spirit which did credit to his conscientiousness. (13.8)
Henchard clearly thinks it is his duty to remarry Susan, even though he doesn't really care for her anymore. His "conscientiousness" and sense of duty are strong enough to force him to do what he can to make amends for the past.
Poor thing – better you had not known me! Upon my heart and soul, if ever I should be left in a position to carry out that marriage with thee, I ought to do it – I ought to do it, indeed! (18.9)
Again, Henchard feels that marriage is a matter of duty – something he ought to do to make amends for the past.
It was an odd sequence that out of all this wronging of social law came that flower of nature, Elizabeth. Part of his wish to wash his hands of life arose from his perceptions of its contrarious inconsistencies – of Nature's jaunty readiness to support bad social principles. (44.8)
This is a funny way of describing the wife sale – it was a "wronging of social law." Note that the narrator doesn't call marriage a "moral" or "religious" law. It's purely a social institution.