Why is the entire community going to the auditorium in chapter 6-10 in the giver?

For the yearly Birthday Celebration. Children turn an older age and the oldest children are given their jobs.

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Answer 2: The first answer is correct, but to reWord it, it is because everyone must attend the ceremonies (that's also when everyone celebrates their birthday- which has to be in December). The children who are turning 12, get an "assignment" or job.