Wilde gets a kick out of Miss Prism. His own sons had governesses that he disliked, and he seems to channel all that aggression (good-naturedly) into her character. Romantic, repressed, and in love with the country priest, Miss Prism really could be the heroine of a Victorian novel.
We first see Miss Prism in her role as educator, which she takes very seriously. As an unmarried woman in a society obsessed with marriage, Miss Prism takes her job as her identity. It gives her some status, when she normally would have none. She uses a lot of flashy vocabulary – "utilitarian" (II.1) and "vacillating" (II.9) – and even tries to impress Dr. Chasuble with made-up words like "womanthrope" (II.81).
Miss Prism springs for the chance to take a walk with Dr. Chasuble. She is totally into him. His sermons, his lectures, his metaphors all make her stomach swarm with butterflies. Cecily clearly recognizes the infatuation and uses it to get out of her lessons. Miss Prism excited to even take a stroll with the preacher, but, in true Victorian style, she hides it beneath fake-scholastic references and roundabout arguments:
But is a man not equally attractive when married?
No married man is ever attractive except to his wife.
And often, I've been told, not even to her.
That depends on the intellectual sympathies of the woman. Maturity can always be depended on. Ripeness can be trusted. Young women are green. [Dr. Chasuble starts.] I spoke horticulturally. My metaphor was drawn from fruits. But where is Cecily? (II.87)
Here Miss Prism is saying that she's attracted to Dr. Chasuble, she wants to marry him, and she’ll continue to be attracted to him once they’re married. Oh, and stay away from those young women, they don’t know anything when it comes to love. Chasuble hears what she’s really saying underneath the banter – that’s why he starts. She’s put a toe just over the line of propriety. But she quickly recovers and reverts to governess mode, asking for Cecily. Chasuble gets enough of the message, though, to embrace her, and effectively propose at the end of the play.
Wilde gets a lot of comic mileage out of Miss Prism’s lack of maternal instincts. For one thing, she is ready to wash her hands of this whole Ernest character. "After we had all been resigned to his loss, his sudden return seems to me peculiarly distressing" (II.137). Ernest seems so wayward, and Miss Prism believes that they are better off without him. And besides, he deserved it: "As a man sows, so shall he reap" (II.107).
There’s also her hilariously cold reaction to Jack at the end of the play. He’s just found out she owned the handbag in which he was discovered at the train station, and he runs to her:
[In a pathetic voice.] Miss Prism, more is restored to you than this hand-bag. I was the baby you placed in it.
[Embracing her.] Yes . . . mother!
Miss Prism: [Recoiling in indignant astonishment.] Mr. Worthing! I am unmarried! (III.146-149)
Not only unmarried, but definitely not willing to be called "mother" under any circumstances.
Miss Prism's nurturing deficit is what caused all the trouble in the first place. "Miss Prism" sounds a lot like misprision – the "neglect or violation of official duty by one in office" (Thanks, www.dictionary.com). Miss Prism was the absentminded babysitter so lost in fictional fantasies that she forgot about young Ernest Moncrieff in his stroller. That’s a crime of misprision if we ever saw one.