June 6th, 1994 of Our Daily Bread had this story:
According to a Greek legend, in ancient Athens a man noticed the great storyteller Aesop playing childish games with some little boys. He laughed and jeered at Aesop, asking him why he wasted his time in such frivolous activity.
Aesop responded by picking up a bow, loosening its string, and placing it on the ground. Then he said to the critical Athenian, “Now, answer the riddle, if you can. Tell us what the 
unstrung bows implies.”
The man looked at it for several moments but had no idea what point Aesop was trying to make. Aesop explained, “If you keep a bow always bent, it will break eventually; but if you let it go slack, it will be more fit for use when you want it.”
People are also like that. That’s why God had given up a time to rest even before we began our work in Gen. 2:2-3. As Pastor Dennis Marquardt said, “work-ethic” comes from “worship-ethic.”
We should take time to relax physically and renew ourselves emotionally and spiritually in God. Jesus said in Matt. 11:28, “Come to Me, all you who labor and are heavy laden, and I will give you rest.” So take time to loosen the bow.