What is the theme in Phantastes by George MacDonald?

Nature is an obvious theme throughout the book. Nature is the perfect place for the imagination to run wild. In the eyes of young children the world around them can become a safe haven from imagined and real, monsters. In the next instant the landscape can change into a terrifying world of shadows and trees that chase one into caves. Nature also serves to reveal otherwise unknown wonders. Anodos discovers a beautiful woman after her rock enclosures allows itself to be broken open through song.