Mr. Knightley keeping no horses, having little spare money and a great deal of health, activity, and independence, was too apt, in Emma’s opinion, to get about as he could, and not use his carriage so often as became the owner of Donwell Abbey.
 

Mr. Knightley prefers to walk to events and parties rather than take his carriage, as he’s perfectly fit to walk long distances and doesn’t care to spend his money on unnecessary things. However, Emma feels that his behavior is unbefitting of the owner of Donwell – she believes that a gentleman should show his wealth and status by arriving in his carriage, rather than on foot, which would be the general transportation method of middle and lower-class people. Fortunately, Mr. Knightley is a confident man and willing to eschew some societal traditions despite what others might think, but many in Emma’s social circle are incredibly limited in their behavior and freedoms by the rules of decorum. These rules are so stifling that Mr. Knightley cannot even walk to a party without being judged. Emma would have Mr. Knightley give up the joy and physical benefits of walking just for the sake of propriety and upper-class lifestyle expectations.

How much his business engrosses him already is very plain from the circumstance of his forgetting to inquire for the book you recommended. What has he to do with books? And I have no doubt that he will thrive, and be a very rich man in time—and his being illiterate and coarse need not disturb us.

When Harriet meets Mr. Martin and stops to converse with him, he tells her that he was so busy on his last visit to Kingston that he forgot to pick up the book that Harriet had recommended him. Emma uses this against him to make him appear unattractive to Harriet, implying that Mr. Martin didn’t get the book because he is unrefined and even illiterate. In reality, Mr. Martin’s admission of forgetting the book means no such thing, and shouldn’t have been taken personally. His honesty and openness have been ill-used by Emma to spin false narratives. But compare Mr. Martin’s bluntness and honesty with the ridiculous flattery of Mr. Elton. Where Robert Martin finds nothing offensive in honestly telling Harriet that he forgot her book, Mr. Elton exaggerates his praise of Emma past the point of believability and rushes to gallantly fulfill gentlemanly duties toward her to win her affection. In the end, Mr. Elton’s overdone romantic gestures are empty, but Mr. Martin’s love for Harriet, while plain and without frills, is genuine.

It is only by seeing women in their own homes, among their own set, just as they always are, that you can form any just judgment. How many a man has committed himself on a short acquaintance, and rued it all the rest of his life!
 

In this passage, Frank Churchill comments on how difficult it is to truly get to know a woman without spending time with her in her natural state, with her friends, and in her home. Indeed, during this time period, many men and women would have married without having intimate knowledge of their partner. Rules of decorum kept men and women from meeting in private, meaning that couples had very little time alone before marriage. This passage also has another layer. Frank is taunting Jane Fairfax by implying that he has engaged himself to her too quickly and is now realizing that he doesn’t know her and will regret their marriage. Had Frank been allowed to express his interest in Jane from the start, rather than resorting to secrecy due to the pressure from his family to marry someone of his class, they would not have had to suffer the anger and miscommunications that plagued their engagement.

“Not for the world,” said Emma, smiling graciously, “would I advise you either way. You must be the best judge of your own happiness.”

Emma means the exact opposite of what she claims here. She most certainly intends to influence Harriet to refuse Robert Martin. She has already made it clear that she does not approve of the match, and now she’s using manipulative tricks – like pretending she doesn’t mind what Harriet’s choice is – to get Harriet to fall in line. Class was so paramount in their society that people like Harriet might put their own happiness aside in order to please their wealthy friends. The classist beliefs of the time period dictated that wealthy people were not only more educated but also innately wiser, smarter, and more trustworthy than the lower classes. There is no doubt that Harriet has been brought up learning these exact beliefs, which causes her to put the opinions of the wealthy Miss Woodhouse over the reasonings of her own heart and stifle the obvious romantic feelings she holds toward Mr. Martin.