In the society the order is that each kid was supposed to get their job but that was changed when Jonas was skipped in the ceremony of twelve role. He received the job as the receiver at the end of the ceremony. This is a job that people don't really get to do. This different job made Jonas feel nervous and scared. This is an important job which causes Jonas to have more responsibilities and forces him to be more of an adult.
Ceremony of Twelve
This is when Jonas receives his first memory. This causes him to change as the memory changes his perspective on the world. He receives a memory of snow and sledding, things that he has never done and seen before.
Jonas receives a memory of war, where a kid was in pain, on the verge of dying. The kid was very injured and was begging for water. This is Jonas's first experience of pain which caused him to be cautious and grateful. It also caused him to be in a short state of depression. It made him want to quit his job as the receiver
Finding out about the Releasing
This is when Jonas sees his father kill one of his patients, a baby. Jonas sees that that his father is barely phased by the fact he just killed a baby. This causes Jonas to believe that everyone in his community is clueless and unaware of what is right and wrong.
Jonas plans to escape to the wilderness with Gabriel. This is a very risky task that could end up with him being killed but he does it for his community. Jonas succeeds and he explores the world and gets to experience new things. This shows a changed Jonas as he is now completely independent and risking his lives for others.
The resolution when Jonas and Gabriel use their last bit of energy to climb up the hill to the sled that leads them to the lit up house with lights. This shows how persistent and independent Jonas has become.