Why is it necessary to earth metallic appliances? What is the function of an earth wire?

Earthing of a metallic appliance is done by connecting a metal wire to the earth, because the earth is at zero potential. This is done to avoid the risk of electric shocks. This is because when live wire at the high potential of 220 volts touches the metal case of the electrical appliance, then the current passes from the electrical appliance directly to the earth through the low resistance earth wire. Since the current does not pass through our body, we do not get an electric shock. Thus, the function of an earth wire is to provide an easy passage to the leaking current from an electrical appliance to go into the earth and hence prevent electric shocks to the user of electrical appliance.