The parasympathetic nervous system is responsible for the body's rest and digestion response when the body is relaxed, resting, or feeding. It basically undoes the work of sympathetic division after a stressful situation. The parasympathetic nervous system decreases respiration and heart rate and increases digestion. (Sciencedirect.com)
If the PNS is operating correctly, it returns our bodies to a harmonious state. This allows us to recover, and prepare for the next stressor.