Talking about Miss Prism we have to start with the information where she works – she is the governess of Cecily. She is educating Cecily to have no imagination or sensationalism in her life. She was working on her family since very early ages, and that is why she is very honorable there.
Also, as you see, nothing is going on without love line. So, Miss Prism being unmarried, falls in love with Chasuble, though the fact that he is a priest prohibits her from telling him about her feelings directly.
As a governess and a person, Miss Prism is an endless source of pedantic talking, stereotypes, and clichés. She approves Jack because of his rightness and always says what a bad person is his “brother.” Her puritan points of view cause nothing more than laughter sometimes.
If not paying attention to her bad sides, her rigidity, she seems to have soft sides too. Once she even wrote a manuscript, but it was not approved. So, maybe exactly where she wanted to write something very personal and to open herself from another side? Because what can be another reason to abandon manuscripts of such a right person?
This woman is a symbol of Victorian moral righteousness. She plays a role of the ideal woman. Unfortunately, not a great amount of people need ideal stuff. She becomes the source of Jack's revelation about his parents.
This woman is kind of an example of the person you’d better not to be. Think for yourself, but do you want to be forever alone just because you have some prejudices which only you understand? Miss Prism was that kind of people we can now call “oh I will not do that because what people will think about me?” Yes, don’t do that, act the way only you want.