Jonas and his father worried about Gabriel's fretfulness at night because if Gabriel can't sleep soundly, that means he is not going to grow and be healthy so he will released.

Release

He put the bed on his room

In their perfect community where everyone must live by certain rules or be "released" (excluded) and out on their own. They fear that if they can't get the baby's fretfulness under control then no family unit will want him and he will be released even though he is a baby that cannot fend for himself.

Jonas and his father are worried about Gabriel's fretfulness at night because it is a sign that Gabriel may not be adapting well to the community's rules and routines. Gabriel's fretfulness could also indicate that he is struggling to adjust to his new environment and may not be thriving as expected. Additionally, his nighttime fretfulness could disrupt the community's sense of order and harmony.