The idea of the law is to move the Sabbath day away from Saturday, which is the last day of the week or the seventh day. The Roman Catholic Church forced a change in the empire in 321 A.D. when Emporer Constantine changed the day of observed worship from Saturday to Sunday. This is to show worship to Lucifer on the first day of the week, disregarding the fourth commandment and blaspheming God.
Of the major religions, Islam, which is a created offshoot of Catholicism, changed it's day of worship from Saturday to Friday. Those who practice Judaism still worship on Saturdays, a point of reference that reinforces the concept in their minds that they are the only ones on Earth doing the right things.