In Act IV, Scene I, Prospero decides to put on “a show,” using magic, for Ferdinand and Miranda. He summons the spirits of Juno, Ceres, and Iris. Iris, the goddess of the rainbow, calls Ceres, the goddess of agriculture. Juno arrives last, but she is the most important, as she is the goddess of marriage and childbirth.
The goddesses commence to bless the marriage of Ferdinand and Miranda. Juno promises: “Honour, riches, marriage-blessing, Long continuance, and increasing.. “ and Ceres promises: “Earth's increase, foison plenty, Barns and garners never empty, Vines and clustering bunches growing…” After the goddesses depart, Iris conjures up some nymphs and land reapers and there is music and dancing. “Answer your summons; Juno does command: Come, temperate nymphs, and help to celebrate "A contract of true love; be not too late…” The nymphs appear; she then summons the reapers: “You sunburnt sicklemen, of August weary, Come hither from the furrow and be merry…” The nymphs and reapers dance until Prospero realizes that he has forgotten the plot against his life, then they vanish.
The purpose of this scene and the masque is to show that Prospero is pleased by the marriage between Ferdinand and Miranda; so pleased, in fact, that he is using his magic, for once, to do something good. The goddesses he calls bless the marriage with fertility and happiness. It is Prospero’s wedding present to the two. It is also speculated that Shakespeare put this in to honor King James, whose daughter had just been married.