Rest is good for the body and the mind.
Humans Need Rest
Rest is an opportunity to disconnect and have downtime. We as humans need it. We are not machines. We have a rhythm to our existence. We respond at different times to the changing circumstances within and without us.
We don't operate at a constant level for long at all. We have ups and downs. By resting, we can embrace the "downs" and allow for sooner, stronger "ups".
For the Body
Our bodies run out of energy. We need to refuel. Disregarding the feedback of one's own body can only last so long. Soon the body will make its own demands on us. This may materialize in the form of sickness. If we can work, eat, and rest more in alignment with our body's need, we will keep it in better form for the things that matter to us.
For the Mind
Our minds drain just as the rest of our physical body. Our mental capacity that we need so much will ebb and flow. We need to replenish this capacity with rest just as with eaten calories for our muscles. Rest allows a disconnect from mental pressure and strain. We can be free for a moment or, as needed, an extended period. We can be ok with being less mentally engaged for a season.
After rest comes rejuvenation of body and mind. We are more ready for the next peak in our rhythm or energy or creativity. Rest is good.