The Yule bell is rang by the royal family of Arendelle to mark the beginning of the Christmas holiday season.
King Agnarr and Queen Iduna would ring the bell with Anna and Elsa when they were young; however, years later, Elsa was the only one to remember the tradition. After the gates were closed, the bell was put into storage and not rung again until the gates were reopened and the kingdom celebrated the holiday season together once more.
In celebration of this, Kristoff and Sven presented the bell to the kingdom, where it was hoisted into position on the castle. Elsa, Anna and Olaf then all rang the bell to mark the start of the kingdom's first Christmas in thirteen years.