Why must father release a new child? Explain.

Are you referring to ch 19? The new child had not lived up to the expectations of being "normal". Jonas watches as his father takes the smaller one and inserts a filled syringe into the newchild's forehead, injecting it while he apologizes to the newborn for having to use his forehead instead of a smaller vein. Jonas waits for his father to clean the child up but instead sees the baby die, and he realizes that his father has killed the twin. Stunned, he sees his father place the body in a carton and send it into a trash chute. The Giver says that he watched the tape of Rosemary's release and saw Rosemary telling them that she would rather inject herself, and he rejects Jonas's suggestion that Rosemary was not brave enough. He, however, could not bear to watch and looked away as she did it. He turns bitterly to Jonas, who feels a horrible sensation of pain.