Interesting to see what the Book of Mormon says about the Sabbath. It is mentioned 3 times: by Jarom (saying they kept the law of Moses), Abinadi (in his sermon on the true meaning of the law of Moses) and Alma the Elder when he formed the church. In 2nd Nephi 25-26 Nephi tells his people they must keep the law of Moses until Christ comes but that then "the words which he (Christ) shall speak unto you shall be the law which ye shall do". Among the Nephites Christ never talks about the Sabbath day but does say "behold, ye shall meet together oft". In 4th Nephi Mormon says "And they did not walk any more after the performances and ordinances of the law of Moses; but they did walk after the commandments which they had received from their Lord and their God, continuing in fasting and prayer, and in meeting together oft both to pray and to hear the word of the Lord". And in his description of the church Moroni says "And the church did meet together oft, to fast and to pray, and to speak one with another concerning the welfare of their souls".
As with other of the ten commandments (thou shalt not kill, thou shalt not commit adultery) Christ doesn't give us the letter of the law but turns the commandment inward letting us decide how often 'oft' should be.
