By an angel. But Clarence the angel rescues George by having George rescue him. It is a humble rather than heroic act. He makes George the hero and himself the fool. By this act of humility he gains his wings.
Life is wonderful.
But it seems we need to be constantly reminded of this fact. This was Chesterton's theme throughout all his writing. For the mind and eyes of the average man this world is as lost as Eden and as sunken as Atlantis. There runs a strange law through the length of human history - that men are continually tending to undervalue their environment, to undervalue their happiness, to undervalue themselves. The great sin of mankind, the sin typified by the fall of Adam is the tendency, not towards pride, but towards this weird and horrible humility.