SABBATH WORSHIP IS A LAW, AND TO BE KEPT HOLY!
Persons who habitually desecrate the Lord’s day cannot be held in fellowship, and members of the Church who neglect public worship and the partaking of the Sacrament and do not remember the Sabbath day to keep it holy, will become weak in the faith and spiritually sickly, and will lose the Spirit and favor of God, and ultimately forfeit their standing in the Church and their exaltation with the obedient and faithful.14
The Lord has said, “Remember the Sabbath day, to keep it holy.” It is a law of God, not only unto this people, but unto all mankind. The member of the Church who does not honor the Sabbath day and keep it holy is in transgression; he continues not in the word of truth; he is not in very deed a disciple of Christ; he will not know the truth, and the truth cannot make him free unless he does know it and live by it.15
Teachings of Presidents of the Church: Joseph F. Smith (2011), 230–39