December is eventful because there are ceremonies in which the children pass through life stages.
In Jonas’s community, children do not have birthdays. Everyone turns a year older on the same day, in December, during the ceremony day. There is a ceremony for each age level from one to twelve. After the age of twelve, no one keeps track any more. After twelve, a person is becoming an adult and treated less and less like a child.
For the youngest children, the ceremony means that they will be assigned a family. Children are not born to parents in the usual way in Jonas’s community. They are artificially created through genetic modification to ensure “Sameness” and then born with surrogate Birthmothers who never see them past delivery. They are then raised in the Nurturing Center by a variety of individuals until they are assigned to family units made up of men and women who can only have two children, a boy and a girl.
Each December, all the newchildren born in the previous year turned One. One at a time--there were always fifty in each year's group, if none had been released --they had been brought to the stage by the Nurturers who had cared for them since birth. (Ch. 2)
So each age group likely has about 50 members (unless some were released due to genetic inferiority or not meeting growth targets as infants). At One they are given a name and a family. From Two to Twelve there is a ceremony each year. Each year they are given something. The "gifts" given vary from a haircut to a bicycle. Many years they get new types of clothing intended to help them grow up.
The most important ceremony is the Ceremony of Twelve. This one is the last one, and it is the one in which citizens are given the jobs they will have for life. All children begin volunteering in the community at eight years old. Between this and input from teachers, and the fact that they are basically spied on constantly, the Elders assign each child a job.
There was no way, really, to know in advance. It was a secret selection, made by the leaders of the community, the Committee of Elders, who took the responsibility so seriously that there were never even any jokes made about Assignments. (Ch. 2)
So in Jonas’s world, not only do you not get to choose your job, and you do not know what it is, but you get your job when you are twelve and you never change it. The twelve year olds begin training for their jobs as soon as they learn their assignments. They begin attending school less and training more until finally, they are just working.
Jonas has no idea what his assignment will be because he does not seem to have any special interests or talents. However, it is clear that Jonas is unique. He is thoughtful, and reflective, and has visions. He is not sure what the visions mean, but when he is skipped during the ceremony, he gets nervous. Called up last, he realizes something special is happening. Jonas is told that he is has been selected for his assignment, rather than just assigned like everyone else.
The Chief Elder goes on to list the traits that Jonas needs to have—or gain—to be Receiver of Memory. It is a special job that does not come up often. These are intelligence, integrity, courage, wisdom, and the “capacity to see beyond” (Ch. 8). She goes on to ask Jonas if he has these traits. He realizes that he does, including the last one, because he has had visions. He has one during the ceremony.
Jonas’s world is very different from ours. The citizens have completely relinquished control in the name of Sameness. To prevent discomfort of any kind, they have given over every aspect of their lives to their government. As Jonas learns when he begins his training as Receiver, they are really only kidding themselves into a false sense of security. Their world is one of tragedy, not safety. By eliminating difference and trying to cut out all emotions, they allowed themselves to become unaware of the horror of what they have done—such as releasing infants.