The hypocrisy exposed by the behaviour of Jekyll and Utterson who despite being "austere with himself" behaved with "approved tolerance for others". As he says on the first page he "lets my brother go to the devil in his own way." This typifies the duality of Victorian society which is ostensibly civilised and decent and yet look beneath the surface of Victorian London to see a sewer of poverty and depraved behaviour. The reputations of many middle class men were a veneer which hid a variety of immoral behaviour. Any city, then or now will hide a depressing underworld which polite society denies.
The style of writing is also typically Victorian; formal language, long sentences, lists of adjectives. The theme of the inner psychochology of the human mind is topical for 1886.