The significance of a warm-up before exercising lies in its ability to prepare the body physically and mentally for the workout. A proper warm-up increases blood flow to muscles, enhances flexibility, and reduces the risk of injuries. It gradually raises the heart rate and core temperature, optimizing performance during the main exercise. Including dynamic stretches or light aerobic activities can also help mentally focus and set intentions for the workout. Overall, warming up is an essential step for any effective fitness routine.