Though Miss Prism appears only occasionally in Oscar Wilde's The Importance of Being Earnest, she is crucial to the plot and to Wilde's satire, and the play could not reach its resolution without her.
She holds the secret of Jack's identity. Miss Prism's greatest importance is that she is the key to the mystery of Jack's birth. Years earlier, when employed as a nursemaid in the household of Lady Bracknell's family, she absent-mindedly placed the baby in a handbag and the manuscript of her three-volume novel in the perambulator, then left the handbag at Victoria Station. This blunder is the very origin of the abandoned baby who grew up to be Jack. When Lady Bracknell recognises her, Miss Prism's confession leads directly to the discovery that Jack is the lost son of Lady Bracknell's sister, Algernon's elder brother, and truly named Ernest. Her revelation resolves the entire plot.
She is an object of satire. As the prim, moralising governess of Cecily, Miss Prism represents the pompous Victorian preacher of respectability and hard work. Yet she once wrote a sentimental novel and confuses her manuscript with a baby, and beneath her severity she nurses a romantic interest in Dr. Chasuble. Wilde uses her to mock the hypocrisy of those who preach earnestness and morality while being comically fallible themselves.
She provides romantic and comic balance. Her mutual, coyly disguised affection for the Reverend Chasuble adds a gentle comic sub-plot among the older characters and rounds off the pattern of pairings at the play's end.
She embodies the theme of names and identity. Because her carelessness caused Jack to be misnamed and mislaid, she is bound up with the play's central concern about the importance, and the arbitrariness, of names and origins.
Miss Prism is therefore important as the agent of the play's resolution, as a target of Wilde's satire on Victorian respectability, and as a source of comic and romantic completion.