Jonas and his father were worried about Gabe's fretfulness at night because it was an indication that he was not developing at the rate that was expected and could result in release.
Jonas lives in a world like ours, but not like ours. Children come from birthmothers and are given to mother and father teams after an application process more similar to a job interview than adoption. Jonas's father is a little different. He had the ingenuity and emotion to ask to bring a baby home when it wasn't developing at the rate of the others. He thought "extra nurturing" in a family environment would give the newchild what he needed.
Jonas's father unknowingly sets off a chain of events that alters the entire course of the book, and the community. This is because Jonas and the boy have a connection. He is fretful not because he is weak, but because he is gifted. Jonas recognizes it instantly. He looks at the boy when Lily, his sister, comments that they have the same unusual light eyes. He notices that the child is not a normal baby because of the expression those eyes. They seem to make him look like he has something.
Depth, he decided; as if one were looking into the clear water of the river, down to the bottom, where things might lurk which hadn’t been discovered yet.” (Ch. 3)
Perhaps Jonas's father subconciously noticed it too and connected his son to the baby, feeling pity. Either way, he saved Gabe. The depth was not superficial. Jonas is able to transfer memories to the baby. Gabe has the capacity to see beyond, and it almost doomed him. He is such a special child in a community where special is not allowed that he almost didn't make it past his first birthday. Unfortunatel, it doesn't last. Gabe is scheduled for release anyway. Jonas, having had the training and knowing what release is, takes that as his cue to take Gabe and go. His father? He's only a little disappointed. We saw him murder a newborn in cold blood. We expected nothing more.