I interpreted it as what one sees in mainstream media affects their perspective of the world since as they begin to consume more of it by watching television or movies they unconsciously identify what they see as the societal norm. So for example, people constantly make jokes about how high school is nothing like the movies. The mass majority only expected the movies to hold truth however because in myriads of young adult movies they would see teenagers go to parties, have sex, sneak out the house, and other things a like which normalized those actions. So essentially when someone views media that portrays consistent stereotypes of a particular group, some may tend to associate it with real life.
It clarifies the relationship between Brutus and Mark Antony. It informs the audience about events that took place off stage. It provides background information about Brutus's relationship with Messala.
