A film's trailer plays a key part in its marketing campaign. Trailers for films based on original screenplays need to convey the film’s genre and give a sense of character and plot to appeal to potential audiences. Trailers for films based on well-known 'classics', such as Great Expectations, must do all these things and more.
For audiences who don't know the story, the trailer needs to give basic plot and character information but for those who know it and who may have seen other adaptations, it needs to convey a sense of the film’s style and the director's interpretation, as well as offering information about production including casting choices. Those who already know the story will be looking to see which actors have been chosen for which roles, and how well these fit with their own expectations of the film.