What does Goldsmith wants to convey through his play She Stoops to Conquer?

In this exquisite comedy of manners, Goldsmith seeks to lay bare the many hypocrisies and double standards at the heart of upper-class English society. In particular, he wants to draw attention to the enormous gap between how the characters perceive themselves and how they really are.
On the face of it, Sir Charles Marlow is the epitome of social respectability. In the rarefied surroundings of a high society gathering, he always conducts himself with the utmost reserve and decorum. Yet when he's in the company of the lower orders, he lets his hair down, laughing, drinking, and carousing with the best of them.
It's only by "stooping to conquer"—that is to say, disguising herself as a barmaid to win Sir Charles's love—that Kate is able to get a glimpse of his true self. Like just about everyone else in society, Sir Charles puts on a false persona, hiding his true personality behind a mask of respectability. Goldsmith, like his heroine Kate, wants to remove that mask and in doing so, reveal what the English upper-classes are really like, warts and all.