Oath to Order

From Zelda Wiki.org

In Majora's Mask, the Oath to Order is a mystical ballad taught to Link when he rescues the first of the Four Giants from Woodfall Temple during his quest to save Termina from Majora's Mask and the falling Moon. It is used to call the Four Giants on the eve of the Carnival atop the Clock Tower. Once all of the Four Giants have been freed from their seal, they will come and prevent the evil menace from destroying Termina while Link and Tatl enter the moon to defeat the evil inside Majora's Mask. In the case that not all the Giants have been saved, the ones who have been released from their seal will still come upon calling, but they will not be able to stop the Moon from crashing into Clock Town on their own.