As BBC explains, the main purpose of microvilli is to increase the surface area of the small intestine. With larger surface area, nutrients from food are more readily absorbed into the blood.
As BBC further explains, the food is first broken down by enzymes in the stomach, and the partially digested food is then pushed through to the small intestine. The lining of the small intestine is covered with microvilli, which are best described as microscopic tentacles or fingers, each containing a blood capillary. These capillaries allow the nutrients from chemically digested food to pass through the microvilli into the bloodstream.