Chapter fifteen was about the symbolism of flying. Flying is freedom but can also represent escape. That is what it symbolizes. Usually stories are fiction when you see a character flying, and most times the character or person is either a superhero, sky jumper, crazy, a circus act, suspended on wires, an angel, or heavily symbolic. Flying and Immortality coincide because flying means resisting gravity therefore in a sense it represents immortality and how there is nothing blocking you from earth and beyond. Or for example as you gradually get older gravity pushes on you year after year . But if you were to beat gravity you would fly high and not have old age. You could also spiritually fly away which could mean death or even freedom from this
