This represents a crucial point in the narrative because this is when Jonas learns the truth about his father, the true meaning of the euphemism "release" and the inhumanity that characterises his community. Key to note is the way that during this chapter, chapter nineteen, Jonas at first keeps on expecting a good ending to what he sees, interrupting the description of the video with his thoughts about what is to happen next:
Now he cleans him up and makes him comfy, Jonas said to himself, aware that the Giver didn't want to talk during the little ceremony.
However, as he looks at the body of the twin, Jonas remembers another vision he had seen, thanks to the Giver:
Once again, as he had on the playing field, he felt the choking sensation. Once again he saw the face of the light-haired, bloodied soldier as life left his eyes. The memory came back.
He killed it! My father killed it! Jonas said to himself, stunned at what he was realising. He continued to stare at the screen numbly.
So, at first, Jonas is completely numb as he realises the truth of what his father had done. When the Giver tells Jonas about the release of Rosemary, his predecessor, Jonas experiences a real internal pain and confusion:
Jonas felt a ripping sensation inside himself, the feeling of terrible pain clawing its way forward to emerge in a cry.
Jonas has just had his entire world turned upside down. Everything that he has believed in has turned out to be false, and what is more, his father, who he had loved and trusted, is shown to be a monster. Understandably he feels great pain and hurt.
This is the moment that Jonas realizes that he sees things completely differently than the rest of the Community. Jonas' father is the one who injects the child with poison and sends it off to the place no one knows anything about outside of their Community, but he (jonas' father) does not have any memories of pain, so he doesn't realize what he is doing to that child. Jonas sees it all happen and is horrified because he finally understands what the Giver has been trying to teach him with the transfer of all those memories- that them two alone are the only ones who truly know the difference between the true world and the illusion the others in the Community are forced to live in by the elder's council.