What day is the Lord’s Day?
The Bible uses the phrase the “Lord’s day” only once in Revelation 1:10, so we know the Lord does have a special day. But there is not one single verse in the whole Bible that refers to Sunday as the “Lord’s Day.” However, the Bible does plainly identify the Sabbath as the Lord’s Day. The only day ever blessed by the Lord or claimed by Him as His holy day is the Seventh day Sabbath. Matthew 12:8 “For the son of man is Lord even of the Sabbath day.” Jesus did not say I AM the Sabbath, or I am LORD Sabbath! Jesus said, “I am Lord OF the Sabbath!”
It was Jesus who made the Sabbath at creation and is the reason for His claim to be Lord of the Sabbath day. (Mark 2:28) If Jesus is the Lord of the Sabbath day, then the Sabbath is the Lord’s Day. The vision John had on “the Lord’s day” according to Revelation 1:10 had to be the Sabbath. It is the only day so designated and claimed by God in the Bible. In writing the Ten Commandments, God called it “the Sabbath of the Lord.”
Lucium who was an early church historian wrote, “In the year 325, Sylvester, Bishop of Rome (AD 314-337), officially changed the title of the first day, calling it the Lord’s day.” (Lucium, Historia Ecclesiastica, p. 739) One would ask why Sylvester would make any claim about changing the title of the first day if the term “Lord’s day” was already widespread before his edict.
It was in fact early in fourth century when Sunday was officially named the “Lord’s Day” which was about 200 years after some of the so called early Church fathers in Alexandria and Rome first changed to Sunday in fear of persecution and against God's will. Note carefully the following Catholic quote:
“St John speaks of the Lord’s day (Rev 1:10) but he does not tell us what day of the week that was, much less does he tell us what day was to take the place of the Sabbath ordained in the commandments. St. Luke speaks of the disciples meeting together to break bread on the first day of the week. Acts 20:7. And St. Paul (1 Cor 16:2) orders that on the first day of the week the Corinthians should lay in store what they designated to bestow in charity on the faithful in Judea: but neither the one or the other tells us that this first day of the week was to be henceforth a day of worship, and the Christian Sabbath; so that truly the best authority we have for this ancient custom is the testimony of the church. And therefore those who pretend to be such religious observers of Sunday, whilst they take no notice of other festivals ordained by the same church authority, show that they act more by humor, than by religion; since Sundays and holidays all stand upon the same foundation, namely the ordinance of the (Roman Catholic) church.” — Catholic Christian Instructed, 17th edition, p. 272-273.