What is the theme in Surprised by Joy by C. S. Lewis?

The value of friendship is a major them in the book. Throughout his life, Lewis was shown the value of being one of a pair or of a "happy few" to his education. His brother was the first of his companions, and the two of them leaned on each other heavily during their mother's illness and following her death. It was their friendship that allowed them to keep their joy and perspective when the adults in their world were essentially destructive influences. Arthur followed him, and was the first to share Lewis' love of literature, but was also able to broaden Lewis' appreciation of nature, the countryside and music. Being familiar with the role as a part of a small group unlike the culture in the main, Lewis befriended others who shared his peculiarities, as demonstrated by his friendship with the boys who shared his love for poetry and plays at Chartres.