This scene is dramatically important in several ways. First, notice that though Olivia is technically in charge, there's not a clear hierarchy at all times. Instead, the clown rebels. Second, notice that the clown and Malvolio take turns insulting one another. This foreshadows how Malvolio will be made into a clown later in the play. Third, the love plot develops, as Olivia late in the scene tells the audience that she's attracted to the messenger. This establishes much of the later tension and comedy in the play, and, combined with the clowning, establishes that everyone in the play will be a figure of fun in some ways.