The primary role of hydrochloric acid in the stomach is to create an acidic environment necessary for digestion. By maintaining a low pH, hydrochloric acid activates the enzyme pepsin, which is responsible for breaking down proteins into smaller peptides. This acidic environment also helps kill harmful bacteria ingested with food, acting as a protective barrier. Furthermore, it facilitates the absorption of certain nutrients, such as iron and calcium, which are essential for various physiological functions.