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Jonas's father is a Nurturer. His job is to provide care for newly-born infants until they are named and assigned to a family unit. He was probably assigned this job because the Committee of Elders recognized qualities of patience and deep caring in him. The fact that he chose to spend much of his volunteer time in the childcare center prior to his Ceremony of Twelve was also undoubtedly noticed.
One of the infants still living under the care of the Nurturers at the time The Giver opens is not growing and developing at the normally-expected rate. This boy baby is not gaining weight or sleeping through the night. Jonas's father recognizes that part of his job is to make decisions regarding the infants in the community, including determining which of a pair of twins will live and which will be "released". However, he finds himself unable to remain objective toward this struggling child and devotes extra attention to him, learning the name planned for the baby ahead of the naming and bringing Gabriel to his living quarters at nights in a highly unusual attempt to give the child more time to thrive.