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

Another prominant theme in the book is the value of reading. Lewis' lifelong devotion to ravenously devouring whatever good literature, poetry and exposition he could get his hands on shows itself to be a distinctively valuable moulder of his mind over the course of this book. In his childhood, his books provided Lewis both with and escape from the sadness of his childhood and with the tools to create the imaginary world that became itself room for him to play. In his boyhood, he explored fantasy and English novelists, then the Norse mythology, then poets and philosophers, the Greek classics and an ever-broadening collection of thinkers. At every stage of his taste and curiosity, he exhausted everything he could find in the category.