During her short life, Jane Austen was a prolific writer of letters, yet few survive. It is widely known that a majority of Jane's letters were burned by her sister Cassandra and destroyed by other members of her family. Their reasons were varied. This excerpt from Jim and Ellen Moody's website: English and Continental Literature, discusses the destruction of these letters and the reasons for it:
Not all the Austens of Jane's generation and increasingly fewer who belonged to the later generations wanted the family's private papers destroyed. It was not Jane but Cassandra who burnt 'the greater part' of Jane's letters, and she only committed them to the fire when in 1842 she understood her own death could not be far off. Jane's letters to Eliza and Henry and hers to them were left in Henry's hands, and they have not survived. However, Frank, throughout a long mobile life, carefully preserved Jane's letters to his first wife, Mary Gibson, and her packets of letters to himself and to Martha Lloyd (who became his second wife). It was Frank's youngest daughter, Fanny-Sophia, who destroyed these and she did so after her father's death (Family Record, p. 252). She acted without consulting anyone beforehand because by that time mores had changed and other of Frank's children and grandchildren would have objected. Happily Philadelphia Walker had no direct descendants who felt their reputations or self-esteem put at risk by the existence of Eliza's letters to her, and she lived long enough so that upon her death these letters fell into the hands of someone disinterested enough to save them, though in a somewhat mutilated state. A record of Jane Austen's great-grandmother, Elizabeth Weller Austen's steady courage, which enabled Jane's branch of the family to maintain the status of gentleman and amass wealth and prestige, survives in a seventeenth century manuscript because several generations of Austens who descended from her second oldest son, the attorney, Francis Austen of Sevenoaks, preserved it (Austen Papers, p. 2).
As a result of the destruction of Jane's own words, biographers have over the years come to widely different conclusions about Jane's thoughts and motives. Ellen Moody outlines some of these varying interpretations in the link I have provided.
To read Jane's letters, click on the following sites: