The primary function of grease is to reduce friction and wear between moving parts. By forming a protective layer on surfaces, grease minimizes direct metal-to-metal contact, thus prolonging the lifespan of components. This is particularly important in applications where relubrication is challenging or impossible, such as in sealed bearings or high-load environments. Additionally, grease can act as a barrier to contaminants like dust and water, preventing them from reaching critical components and causing damage.