Jonas is so anxious about his new position because it is so unlike any of the others, which in his society is taboo. First of all, he is skipped over and then singled out at the ceremony, which signals that this is no ordinary job. Then he gets certain rules that tell him that he can break cardinal rules of the society, such as he is allowed to lie. Then, he is informed that his job may cause him pain and he isn't allowed to seek treatment for that pain, and that he is not allowed to talk about his job with other people. All of these reasons are quite enough to scare anyone, let alone someone like Jonas who lives in a society where there is no pain, no suffering, and no secrets (or so he thinks).