As I wrote before, there are few significant themes which should be stressed out.
At the very beginning of the play, Wilde introduces his time society, in particular their lifestyle and the high-class manners, with one of the major characters - Algernon whose ideas about life are rather superior and it may seem that Wilde protraits himself in this particular character. Algernon brings up topics such as marriage which he dispises and underlines its flaws, he was once married and as he says "it was in a consequence of a misunderstanding between myself and a young person". ( page 7) Obviously, Wilde did not like the generally perceived view of wedlock. In Victorian Era and I´d say even nowadays, marriages don´t mean much to people, in case they do, it is mostly at the beginning, when the time passes married couples tend to seperate, and degrade each other to a position of an absolute certanity or some piece of furniture. It will stay wherever you leave it. Take this as an evidence " The very romance is uncertainty. If ever I get married, I´ll certainly try to forget the fact." or "...in married life three is company and two is none."
However the major and simultaneously most profond topic-theme is the importanc eof being earnest, or better to say not being earnest. Throughout the entire play one encounters countless numbers of scenes, moments, dialogs in which Wilde emphasizes the ridiculous obsession of the whole society to BE IMPORTANT. He prsents the contorversy of triviality and seriousness. What SHOULD be important or taken seriously is not and the other way around. For example Algy is much more worried about cucumber sandwiches than the social issues.
Lady Bracknell who will thouroghtly examine each suitor´s origin to make sure he comes from the RIGHT background. Also the idiotic idea developed by Gwendolen that she has always wished to married someone named Ernest? - see Wilde´s ironic hint? Therefore she is even more enthusiastic about marrying Jack-Ernest.
The way I comprehend this play is people would fake their life stories, characters, they would invent alter ego and do God knows what mindless things just to have resonant reputation and admiration of their surrounding. How pathetic is that?????