Jonas is worried about the Ceremony of Twelve.
There are a lot of different things Jonas is worried about at different times during the book, but I think you are talking about the beginning of the book, when Jonas says he is apprehensive. He goes through a series of words, trying to decide which emotion it is. Is it “frightened,” or “distraught,” that he feels? No, these are not the right emotions.
He was eager for it to come. And he was excited, certainly. All of the Elevens were excited about the event that would be coming so soon. But there was a little shudder of nervousness when he thought about it, about what might happen. (Ch. 1)
Jonas settles on the word “apprehensive” to describe his feelings. He is worried because he is passing a major milestone for his community, and he does not know what is in store for him. He is going through a ritual that will end his childhood, and start to give him the responsibilities of an adult. What he does not know is that this ceremony is going to end his innocence forever.
During the Ceremony of Twelve, Jonas will be assigned a job that he will have for life. Every eleven year old will. One of the reasons that he is nervous is because he has no idea what that job will be—he does not get to choose it or have any say in one it is. It is assigned by committee, secretly, based on years of aptitude tests, intelligence screenings, and observations—and there is no appeal.
"I know there's really nothing to worry about," Jonas explained, "and that every adult has been through it. I know you have, Father, and you too, Mother. But it's the Ceremony that I'm apprehensive about. It's almost December." (Ch. 1)
Unlike so many of his friends, Jonas seems to have no special interests or aptitudes. He doesn’t have an inkling what will happen to him. Thus, the nervousness. Jonas realizes that it is a part of life in his community. He explains to his father and mother, two adults that he is not related to who have been chosen to raise him, why he is nervous.
Jonas has reason to be nervous. He is selected as the Receiver of Memory, the recipient of the community’s pain and suffering. He will store its memories and its wisdom, and be the one they go to when they need to make decisions. Jonas turns out to be different though. After Jonas is made Receiver, he has a lot more to worry about. This is a community that has locked away emotions and eliminated hunger and pain, but it has also banished love and humanity.
When Jonas finds out that the community regularly murders citizens who break the rules or do not conform to its rigid and narrow view of Sameness, even infants like the innocent Gabriel, Jonas has to make a choice. Will he continue to be obedient and careful, or will he take a chance, and break the community’s chains?
This is the story of a world where discomfort is not tolerated. The first chapter alone tells us that. Jonas seeks carefully for a word to describe how he feels. His parents seek to identify his feelings, not to comfort him for the feelings, but to banish those feelings from him. What Jonas's community has not realized is that while feelings are hard to cope with, they are what make us human, and we must learn to take the good with the bad. This is the lesson Jonas decides to teach them and the reason he flees.