In Roald Dahl's book "Matilda," the theme emphasizes that a person's character greatly influences their life. The quote, "If you are good, life is good," suggests that positivity and kindness can shape one's experiences and outlook. Matilda, the protagonist, is portrayed as exceptionally intelligent and good-hearted, overcoming challenges through her inherent goodness.

This message resonates throughout the story, highlighting the power of goodness in transforming not just one’s own life but also the lives of those around them. Matilda's journey illustrates how moral integrity and resilience can lead to a fulfilling life despite adversities.