"The Lord's Day" and the Sabbath

Lord's Day.  (Bible Dictionary) 

Occurs in the Bible only in Rev. 1:10.  The first day of the week is meant, being the day of

our Lord's resurrection and also the day on which the Holy Spirit came upon the apostles.

References to its weekly observance are found in 1 Cor. 16:1–2; Acts 20:7; and in many

early Christian writers.  It was never confounded with the Sabbath, but carefully distinguished from it (e.g., Col. 2:16).  The term is used also in D&C 59:9–13.

Adam Clarke's Bible Commentary 

Rev. 1:10 - "The Lord's day" - The first day of the week, observed as the Christian Sabbath, because on it Jesus Christ rose from the dead; therefore it was called the Lord's day, and has taken place of the Jewish Sabbath throughout the Christian world. 

Acts 20:7 - "Upon the first day of the week" - What was called kuriakh, the Lord's day, the Christian Sabbath, in which they commemorated the resurrection of our Lord; and which, among all Christians, afterwards took the place of the Jewish Sabbath. 

Easton's Bible Dictionary 

The change of the day. Originally at creation the seventh day of the week was set apart and consecrated as the Sabbath. The first day of the week is now observed as the Sabbath. Has God authorized this change? There is an obvious distinction between the Sabbath as an institution and the particular day set apart for its observance. The question, therefore, as to the change of the day in no way affects the perpetual obligation of the Sabbath as an institution. Change of the day or no change, the Sabbath remains as a sacred institution the same. It cannot be abrogated. 

If any change of the day has been made, it must have been by Christ or by his authority. Christ has a right to make such a change ( Mark 2:23-28 ). As Creator, Christ was the original Lord of the Sabbath ( John 1:3 ; Hebrews 1:10 ). It was originally a memorial of creation. A work vastly greater than that of creation has now been accomplished by him, the work of redemption. We would naturally expect just such a change as would make the Sabbath a memorial of that greater work.

True, we can give no text authorizing the change in so many words. We have no express law declaring the change. But there are evidences of another kind. We know for a fact that the first day of the week has been observed from apostolic times, and the necessary conclusion is, that it was observed by the apostles and their immediate disciples. This, we may be sure, they never would have done without the permission or the authority of their Lord. 

After his resurrection, which took place on the first day of the week ( Matthew 28:1 ; Mark 16:2 ; Luke 24:1 ; John 20:1 ), we never find Christ meeting with his disciples on the seventh day. But he specially honoured the first day by manifesting himself to them on four separate occasions ( Matthew 28:9 ; Luke 24:34 Luke 24:18-33 ; John 20:19-23 ). Again, on the next first day of the week, Jesus appeared to his disciples ( John 20:26 ). 

Some have calculated that Christ's ascension took place on the first day of the week. And there can be no doubt that the descent of the Holy Ghost at Pentecost was on that day ( Acts 2:1 ). Thus Christ appears as instituting a new day to be observed by his people as the Sabbath, a day to be henceforth known amongst them as the "Lord's day." The observance of this "Lord's day" as the Sabbath was the general custom of the primitive churches, and must have had apostolic sanction (Compare Acts 20:3-7 ; 1 Corinthians 16:1 1 Corinthians 16:2 ) and authority, and so the sanction and authority of Jesus Christ. 

Also see James E. Faust "The Lord's Day"