The Question and Answer section for The Importance of Being Earnest is a great resource to ask questions, find answers, and discuss the novel.
Lady Bracknell represents Victorian morality and ethic. She, like a gorgon, is overbearing and unforgiving. She demands that Jack find a decent family and her judgments over marriage prospects are definite.
Ultimately Jack gets what he wants by taking on the identity of Ernest. He has money, social standing, and the girl. He can support a number of themes by exposing his identity.
I have never considered Cecily silly..... she's simply a girl who acts like any other. None-the-less, her writing and avoidance of schoolbooks allow us to infer that she's far more interested in fiction and fantasy than serious thought....