The primary purpose of the large intestine in digestion is to reabsorb water and electrolytes while forming and storing feces. As undigested food passes through the large intestine, the absorption process helps maintain fluid balance in the body. Additionally, beneficial bacteria present in the large intestine contribute to the fermentation of leftover nutrients, producing short-chain fatty acids that promote intestinal health. The large intestine protects the body by preparing waste for elimination, making it a vital component of the digestive system.