This is a quote from M. Denis de Rougemont, and Lewis returns to it many times over the course of The Four Loves. “Demon” (6) can be defined in the book as a love—other than Charity—that has taken supreme importance in the life of the person experiencing it. Eros can be healthy, but not if it has inordinate influence—when it is a “god”(6), as de Rougemont suggests—over someone. The same can be said of Affection and Friendship. This is one of Lewis’s primary aims in The Four Loves: to help Christians see that their loves can in fact be detrimental to their spiritual development unless they are balanced and below Charity. As long as a love is a distraction, it is a demon.

Lewis presents the forms of love between people as a series of give and take relationships. It seems indisputable to him that people frequently give gifts—or time, or work—to those they love. But this is challenging when applying that a relationship with God can have a give and take aspect: how can a mortal give anything to an omnipotent being? The answer is nearly a “paradox” (128): the greatest gift—or the closest thing to a gift—that a person can give to God is to practice Charity towards other creatures and to sacrifice one’s life to God’s glory.