What is Jonas prohibited from doing in Lois Lowry's The Giver? Why?

In Chapter 9, Jonas discovers the rules he must follow while he is a Receiver-in-training. He becomes visibly dismayed when he realizes he will be prohibited from enjoying certain privileges he has always relished.
Accordingly, he is prohibited from sharing the secrets or events of his training with other members of the community, his parents, or any of the Elders. While in training, Jonas is prohibited from mingling with members of the community. According to the Chief Elder, no one can observe or modify Jonas' training. So, the reason for Jonas' seclusion is to prevent any interference from members of the community in Jonas' training.
Jonas is also prohibited from dream-telling, applying for release, or applying for any medication (except for illnesses or injuries unrelated to his training). He cannot apply for release because his selection as the next Receiver of Memory is a rare honor and one he is required to accept. Finally, Jonas must endure "indescribable" pain during his training without pain medication.
As a Receiver-in-training, Jonas cannot apply for medication because he must endure and receive all the painful memories of the past to be successful in his job as the new Giver.
Since Jonas must return to his quarters after Training Hours every day, he must forego his interactions with his friends and refrain from enjoying activities such as playing ball or riding his bike along the river. He definitely feels frustrated that, in his many hours of training, time has not been allocated for recreation.