In Exodus 20:10-11 we learn about how the Lord observed the sabbath day,

“But the seventh day is the sabbath of the Lord thy God: in it thou shalt not do any work, 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 heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the Lord blessed the sabbath day, and hallowed it.”

When the sacrament was introduced as a way for Christian worshipers to venerate Jesus’ atoning sacrifice, Sunday was the day that was appointed to blessed and for worshippers to partake of it. Modern day revelation appoints Sunday as the day of rest and the first day of the week.

In order to commemorate the resurrection of Jesus, several changes were made including the practice of meeting on the first day of the week, Sunday. Jesus set an example of setting this as the day of worship in his initial appearance to the apostles, and then again in a second appearance to those same apostles in the company of Thomas. After Jesus was resurrected, it was on the day of Pentecost, when the saints assembled and received the Holy Ghost.

This change in day of worship was not a difficult change for early Christians. This is easily seen by their continued faithfulness in worship after the change was made. This faithfulness can be demonstrated in Acts 20:7,

“And upon the first day of the week, when the disciples came together to break bread, Paul preached unto them, ready to depart on the morrow; and continued his speech until midnight.”

Constantine officially designated the first day of the week as a day of rest by A.D. 321. The word “Sunday” was generated from the weekly pagan worship of the sun God in Rome.

On August 7, 1831, revelation was received confirming the Lord’s prescribed design in changing the day of public worship. This revelation was received on a Sunday and D & C 59:12 records the revelation,

“But remember that on this, the Lord’s day, thou shalt offer thine oblations and thy sacraments unto the Most High, confessing thy sins unto thy brethren, and before the Lord.”

For members of The Church of Jesus Christ of Latter-day Saints, the day of the week on which they gather to pay devotion to God and his Son matters less than receiving the edification and enlightenment that may be gained from worship. This observation is confirmed, for example, by the Church’s custom of worshiping weekly in countries in the Middle East on a day other than Sunday.

As President Joseph F. Smith explained, Latter-day Saints are to gather on a day to “mingle with the saints that their moral and spiritual influence may help to correct our false impressions and restore us to that life which the duties and obligations of our conscience and true religion impose upon us” (Smith, p. 243; see D&C 59:9-19).