A bird is active, because a bird is soft. A stone is helpless, because a stone is hard. The stone must by its own nature go downwards, because hardness is weakness. The bird can of its nature go upwards, because fragility is force. In perfect force there is a kind of frivolity, an airiness that can maintain itself in the air. Modern investigators of miraculous history have solemnly admitted that a characteristic of the great saints is their power of "levitation." They might go further; a characteristic of the great saints is their power of levity. Angels can fly because they can take themselves lightly.

(Orthodoxy - G. K. Chesterton -  1874-1936)