Prospero tells Miranda their history as a way to inform the audience of this important information. In addition, the audience needs to know what events motivate Prospero's decision to stir up the storm and why the men onboard the ship are his enemies — several share responsibility for Prospero's isolation. By sharing this information, Miranda — and the audience — can conclude that Prospero is justified in seeking retribution. At the very least, Prospero must make Miranda sympathetic to this choice. It is also important that Prospero gain the audience's sympathy because his early treatment of both Ariel and Caliban depict him in a less than sympathetic light.
Ariel and Caliban are both little more than slaves to Prospero's wishes, and, in the initial interactions between Prospero and Ariel and Prospero and Caliban, the audience may think Prospero callous and cruel. He has clearly promised Ariel freedom and then denied it, and he treats Caliban as little more than an animal. The audience needs to understand that cruel circumstance and the machinations of men have turned Prospero into a different man than he might otherwise have been. But Prospero's character is more complex than this scene reveals, and the relationship between these characters more intricate also.
During the course of the story, Prospero repeatedly asks Miranda if she is listening. This questioning may reveal her distraction as she worries about the well-being of the ship's passengers. Miranda is loving toward her father, but at the same time, she does not lose sight of the human lives he is placing at risk. However, his questioning is equally directed toward the audience. Prospero also wants to make sure that the audience is listening to his story, since he will return to the audience in the Epilogue and seek their judgment.
