4 ideas
Thomas escapes into visions, including a gentle, conversational Jesus and imagined Biblical plagues, and keeps a notebook he calls 'The Book of Everything'. The household changes when his mother, backed by a neighbor the father calls a witch and a group of women, openly refuses the father's authority. The father, stripped of submission, loses his power.
The abusive father's power rests entirely on others' fear and compliance, not on any real strength. When the mother and the women around her collectively refuse to obey, his authority evaporates almost immediately.
The Jesus Thomas sees is kind and playful, and he openly distances himself from the fearful, punishing religion of the father. This lets a child keep his faith while rejecting the man who uses faith as a weapon. It treats abusive religion as a counterfeit that hijacks the sacred rather than as a true expression of it.
Thomas resolves that when he grows up he will be happy, which frames happiness as a stance he chooses rather than a circumstance he receives. Under a regime of fear, choosing joy is an act of defiance, because it refuses the emotional terms the oppressor sets. Courage, which Thomas learns from a neighbor who survived the war, is what makes that choice possible.