Air is the element of freedom; The Air Nomads detached themselves from worldly concerns, and they found peace and freedom.
Fire is the element of power; The people of the Fire Nation have desire and will, and the energy and drive to achieve what they want.
Earth is the element of substance; The people of the Earth Kingdom are diverse and strong. They are persistent and enduring.
Water is the element of change; The people of the Water Tribes are capable of adapting to many things. They have a sense of community and love that holds them together through anything.