The family must sign a pledge that they won't get attached to Gabriel when he comes to visit from the Nurturing Center. The rule is that each family unit must have a father and a mother along with only one son and one daughter. The only reason that Gabriel, the baby, is coming home with the father is because he is given another chance to grow and develop before he is either placed with a family or "released." The elders of the community do not want Jonas's family to get attached or else there might be a problem at the end of his time with them. They don't want the family to think that they can keep Gabriel since his fate in the community is unknown and based on his growth and development.