The term "the Lord's day" appears in Scripture just once, in Revelation 1:10 where John writes about being "in the spirit on the Lord's day." He does not elaborate or explain, leading many scholars to conclude that those he wrote to, the early churches, understood and were familiar with the term.
The Lord's Day – What is it?
It is assumed that "the Lord's day" is a reference to Sunday. At that time, Christians gathered together on Sunday to commemorate the day Jesus rose from the dead (John 20:1; Acts 20:7; 1 Corinthians 16:2). Some have suggested that Sunday is the new Sabbath day or the "Christian Sabbath." But this is not so. Jesus demonstrated He is Lord over the Sabbath (Matthew 12:8) and said He came to fulfill the Law. The Israelites were bound to keep the Sabbath by rules, but no rule-keeping can justify anyone (Romans 3:20–30). Christians have been justified by Jesus and His sacrifice on the cross and subsequent victory over sin and death. We are no longer bound to the Old Testament Law, but to Christ. It is this salvation—one apart from works—that we gather together to celebrate and live out (Ephesians 2:8–10; Hebrews 10:24–25). Paul writes that we have freedom regarding a day of rest and worship, among other areas not addressed in the New Testament. "Therefore let no one pass judgment on you in questions of food and drink, or with regard to a festival or a new moon or a Sabbath. These are a shadow of the things to come, but the substance belongs to Christ" (Colossians 2:16–17).
So, no specific day is proscribed as a Sabbath for Christians. As Christians, we should set aside a day of the week in honor of God, to follow His example of rest, and to worship. But Sunday is not the "Christian Sabbath" and the Christian is not bound by the Law (Romans 6:14–15). We are to rely on our conscience to determine when to worship. "One person esteems one day as better than another, while another esteems all days alike. Each one should be fully convinced in his own mind. The one who observes the day, observes it in honor of the Lord. The one who eats, eats in honor of the Lord, since he gives thanks to God, while the one who abstains, abstains in honor of the Lord and gives thanks to God" (Romans 14:5–6).
Some Messianic Jews regard the Sabbath day as holy because of their heritage, and some Gentile Christians honor God by observing the Saturday Sabbath as well. But the day of the week is not as important as the motive behind the choice Christians make to worship God. If a Christian's choice is due to legalism or obedience to the Law, then his heart must be examined (Galatians 5:4). God is pleased when we worship Him in spirit and truth on any day of the week.
Is there a reason most Christians worship on Sunday?
What is the Sabbath? Is the Sabbath day for rest or for worship?
Is Sabbath-keeping something Christians should do?
Is the Sabbath Saturday or Sunday?
What is Christian worship?
Truth about Church