What is the theme in Till We Have Faces by C. S. Lewis?

Love is another theme in the book. The characters in Till We Have Faces debate the complex topic of love, platonic and sexual. Young Orual loves her Greek tutor, the Fox, and half-sister Psyche/Istra above all, but from earliest childhood, Psyche foresees one day marrying the greatest king of all, who will build for her a castle of gold and amber on Grey Mountain. The people love beautiful Psyche briefly when she heals their fevers, but turn fickle and call for her sacrifice. In the crisis, the Fox's love for Psyche overcomes his normal wiles, and Orual's causes her to go out of character to implore the King as "father" to spare her.