Anywhere in the world you travel, you will find that a week is seven days long. During the Russian Revolution, the government moved to extend "a week" by a day but productivity decreased by 30%. The government then moved to shorten "a week" to six days, only to find the same result. When "a week" again became seven days long, productivity returned to its previous level.
This is because God the Creator designed and made a human body's rhythm to be most suitable for each individual to work diligently during the six days of the week and rest on the seventh day.
On those who work diligently during the six days of the week and worship Him by holding sacred the seventh day of the week, God will pour out spiritual blessings of heaven as well as plentiful blessings of this world.

"For six days work may be done, but on the seventh day there is a sabbath of complete rest, a holy convocation. You shall not do any work" (Leviticus 23:3).
~ from Dr. Jaerock Lee's column "The Way" carried on The Seoul Newspaper