Prospero has Ariel arrange a pageant for a couple reasons. First of all, a pageant, or masque, is a typical celebratory ceremony that surrounded a wedding in that time period. Since Miranda and Ferdinand were just engaged to be married, it was customary. Additionally, Prospero didn't really like some of the comments Ferdinand was making about Miranda regarding their wedding night, so he wanted to use the goddesses as a warning to Ferdinand that the civil, familial, and political aspects of marriage are more important than love or lust.
