Why is carbon so important in living things when oxygen is the most abundant?

Carbon is very important in living things because the glucose which is the main source of energy is made up of carbon. All the food we eat contains carbon and its products such as carbohydrates, proteins, lipids and these all contain specific amount of carbon. So all the food we eat breakdowns into glucose which is a six carbon compound and through which energy in the form of ATP is produced and we perform all life activities.