It is clear from the opening chapter of this book that class and social mobility are key concepts that govern the actions of the characters and in particular are massively important when related to marriage and how it can be used as a means to raise your social status, as Mrs. Clay hopes to achieve, but also how it could lower your social status, which is why of course why Anne Elliot is "persuaded" out of marrying Captain Wentworth in the first place. The focus placed on social mobility is one that is highlighted by the following remark by Sir Walter Elliot in Chapter Three when he talks about the Navy and his objections about it:
Yes; it is in two points offensive to me; I have two strong grounds of objection to it. First, as a means of bringing persons of obscure birth into undue distinction, and raising men to honours which their fathers and grandfathers never dreamt of; and secondly, as it cuts up a man's youth and vigour most horribly.
The real problem that Sir Walter Elliot has with the Navy is that it allows men of low birth with very little social status in society to improve their social status through hard work and effort. For such a person as Sir Walter Elliot, who is so obsessed with his birth and family lineage, as the opening lines of the novel indicate, the thought that people of obscure birth could ascend the ranks of society is very unpalatable. Of course, this comment reveals him to be a massive snob, but it also gives rise to one of the central conflicts going on in society at the time: being born into a social hierarchy and the worrying idea (to those occupying the higher rungs of that hierarchy) that people could work themselves up through hard work and personal ability.