Is there more toil? Since thou dost give me pains,
Let me remember thee what thou hast promised,
Which is not yet perform’d me.

– William Shakespeare

The Tempest, Act 1, Scene 2. When Prospero arrived on the island, he freed Ariel from a pine tree where the witch Syforax had imprisoned him. In return Ariel promised to work in the service of Prospero for a year to repay him. In this passage Ariel holds Prospero to his end of the deal, reminding him that the time for his liberty has come. He is only doing Prospero’s bidding in order to gain his freedom.