The primary role of the large intestine in digestion is to absorb water and electrolytes from indigestible food matter. It transforms liquid waste into a more solid form, preparing it for excretion. The large intestine also houses beneficial bacteria that assist in the fermentation of some undigested materials, contributing to the production of vitamins like vitamin K. By managing the balance of fluids in the body and aiding in waste elimination, the large intestine plays a crucial part in maintaining overall digestive health.