Why did The Giver not want to escape with Jonas?

I believe that the Giver did not transmit any "release of pain" because Jonas needed to fully experience what pain was in order to be successful in his training as Receiver. Moreover, I believe that if it had not been for this event in excruciating pain, Jonas would not have rallied up the courage to leave the Community and save his younger adopted brother Gabriel. It also states in his rules that Jonas must not receive release of pain, and the Giver therefore would be breaking rules if he were to.

Also you need to remember that the pain isn't actuallyphysical (he didn't actually break his leg, it's all mental). Pain medication wouldn't help him because the pain is in his head.

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Answer 2:

Because it was indicated in the rules for Jonas's assignment that he is not allowed to take medication.