What is the effect of focusing on Portia in Act II, scene 4 of "Julius Caesar"?
By the way Portia acts in Act II, scene 4, the reader can assume that she has learned of Brutus' plan to assassinate Caesar. She is frantically sending Lucius to the Capitol to check on Brutus and her frantic nature contrasts the more calm nature of the soothsayer.
This scene can serve two purposes. First, it increases the dramatic tension. Portia is frightened and her fear shows the reader how terrible the assassination is. The interaction with the Soothsayer also increases dramatic tension, as it gives the reader the possibility that Caesar may be saved.
Focusing on the irrationality of Portia's thought, speech and attitude (sending Lucius, changing her mind, etc) makes her actions later in the play more believable. (I don't want to tell you what she does, in case you haven't read.)