Remember the sabbath day, to keep it holy.
The Sabbath day was formally given to the nation of Israel for strict observance. It was a picture of the rest believers now enjoy in Christ. The Sabbath is the seventh day of the week, from sundown on Friday to sundown on Saturday. Nowhere in the New Testament are Christians commanded to keep the Sabbath, we are, however, to set aside the first day of the week, Sunday, to honor God.