Answer: "singing loud for all to hear"
We hear this line at the beginning of the movie. The elves are reviewing what to do at the North Pole. During the review, Buddy and the elves say, "The best way to spread Christmas cheer, is singing loud for all to hear." Buddy reminds people in New York about this. At the end of the movie, Jovie sings a Christmas carol, as she understands that the best way to spread Christmas cheer, is singing loud for all to hear.