"Remember the sabbath day to keep it holy. Six days shalt thou labour, and do all thy work. But the seventh day is the sabbath in honour of the Lord thy God; on it thou shalt not do any work, neither thou, nor thy son, nor thy daughter, thy manservant nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates; For in six days the Lord made the heavens and the earth, the sea, and all that is in them, and rested on the seventh day; therefore the Lord blessed the sabbath day, and hallowed it."
The Fourth Commandment--or if you are Catholic or a member of certain Protestant bodies, the Third--as spoken by God to Moses on Mount Sinai in Exodus 20. God rested on the seventh day of creation, and he expects us to as well. It is a way of revering God, revering the world he has made by resting from our daily toil and enjoying it, and preserving our mental and physical health. Jesus once said, "The Sabbath was made for man, not man for the Sabbath." This reminds us once again that the Commandments are not arbitrary rules devised because God likes to see us squirm. These are operating instructions for an authentically human life.