At their first meeting, Harriet finds Augusta 'very charming' and 'quite beautiful' but she learns later to see her as 'very ill-tempered and disagreeable'. This – and her emotional education – prevent Harriet from being colourless. The touching scene in which she destroys her 'Most Precious Treasures' is especially memorable. It is also important for Emma's reactions: it makes her aware of the harm she has caused (when Elton cut his finger, she pretended to have no court plaster and made Harriet supply some) and she realises she herself would never keep as a relic 'a piece of court plaster that Frank Churchill had been pulling about’.
(Incidentally, Jane Austen no doubt derived the germ for the 'Most Precious Treasures' from a letter she received from her beloved niece Fanny Knight: Fanny had visited the room used by the man with whom she thought she was falling in love and had obviously regarded his shaving cloth as a most precious treasure. Jane replied, 'The dirty shaving rag was exquisite! Such a circumstance ought to be in print. Much too good to be lost.')
Harriet is also instrumental in Emma's education. Jane Austen uses the portrait incident to enable the confusion to develop. Later, Harriet is conveniently ill on Christmas Eve, thereby leaving Emma to the company of Elton, who takes his chance and reveals his intentions.
But Emma continues to deceive herself.
There is the ball at The Crown during which Knightley dances with Harriet, and later Harriet's rescue from the gypsies by Frank Churchill. When Harriet speaks of the man she now admires at a distance - and to think of his infinite superiority to all the rest of the world, Emma assumes she is referring to Frank. Having learned well from her previous mistake, she resolves not to interfere this time. She will not even hear the gentleman's name confirmed. Thus she continues to blunder until her painful disillusionment.
When Harriet gives her that great shock and unwittingly teaches her to understand her own emotions, Harriet, once the muddled thinker and timid speaker, proves articulate just when her words are least welcome. Hoping for a proposal from Mr. Knightley, she cites the very argument Emma had put forward when thinking of a marriage between Harriet and Frank: But you know they were your own words, that more wonderful things had happened, matches of greater disparity had taken place.... So Harriet is the catalyst to the emotional climax of the novel.
Harriet has a very important function is making us think about how we should conduct ourselves in our behaviour towards our fellow men, which is a central theme of this novel (and is close to the heart of all Jane's mature writing). Though she lacks Emma's wealth and education, she has greater good-will. Even on the odd occasion when she is obliged to see defects in another (Mrs. Elton), she says, However,... I wish her no evil.