What is the theme in Myths to Live By by Joseph Campbell?

The imprint of mythology on the human mind is the main theme of this book. Campbell deals compassionately even with cultures who performed ritual sacrifice of people living in villages surrounding their own, and burn the wives of dead husbands on the funeral pyre because he understands that man is designed to identify and worship a divine mind, and without formal education available about what the mind our minds long to connect with is, humanity will make something up to fill in the gap. He reaches this conclusion about the human mind after having spent the greater part of his life studying mythologies and finding among them a common mythological structure, and then having the idea presented to him that the very structure he was finding in common between religious mythologies could be present in human dreams and psychoses as well.