What is the role of sand in the novel??

The grains of sand penetrate every crevice and opening of the house, and are in every part of their lives. When they sleep, they place towels over their face so they can breathe comfortably, and when they awake their eyes water from the irritation of the sand. When the grains are moved in a wave by the wind, it creates a huge, destructive, powerful force that no one can halt.