Hebrews 4:9-10

So there remains a (full and complete) Sabbath rest for the people of God. For the one who has once entered His rest has also rested from (the weariness and pain of) his (human) labors, just as God rested from (those labors uniquely) His own. 

There is a culture of busyness that never takes the time to rest. Rest is essential because it helps bring God back into our thoughts and lives. Overwork, stress, and busyness all wear the body and mind down, not build them up. God never intended for us to live a life of exhaustion.