The significance of being given an assignment is that now you are an adult and now you have your life's work picked out and you know what you are going to be.

The Twelves are given assignments because that is how jobs are gotten in this society.  You do not pick your own job -- you are selected to do a job.  If they did not give people assignments, three things would happen:

• Not every job would be filled and there might be competition for other jobs
• The whole idea of sameness would be hurt because people would be competing for the good jobs and not feeling so united with everyone else in the community.
• Life would be harder because people would have to figure things out for themselves -- this would also reduce sameness because it would reduce "government" control.