The Oath to Order is the song used to draw the four giants of Termina to Clocktown to stop the moon from falling. Link learns this song after rescuing the first giant from Woodfall Temple. While the song can be played even without rescuing the four giants, those that have been rescued will fail to stop the moon.
To summon the giants, Link must play this song on top of the Clocktower during the Carnival of Time on the last night. When the four giants arrive and stop the moon, the final battle against Majora's Mask begins.
