He wasn’t not qualified to be Giver himself, nor has Gabriel been selected to be receive it in the giver

These few sentences encapsulate Jonas' predicament. He has received various memories from the Giver, and in his desire to settle Gabriel has shared some of them. What he was doing had no precedent, he wasn't qualified to pass on memories, especially being that he was still in training. And Gabriel..... a mere infant, has not been chosen as a Receiver. In this, Jonas was flouting convention and breaking the rules. He was putting himself in danger, but most of all, he was asserting his individuality.