What is the advantage of prospero narrating the story of antonios usurption of his throne

These sets up the context of the story while letting us discern details about certain characters. Prospero tries to avail Miranda's concern over the violent storm. In doing this, he also gives us a bit of history behind why they are living on an island. We see that Prospero's revenge is the thrust of the play yet his explanation to Miranda is not bitter rather passionate with a touch of pathos. For this we can surmise that Prospero's motives may not be fully vindictive. Prospero seems to have a wise element to him and hence can be afforded a certain amount of trust by the audience.

narrate the story tempest