here has always been a bit of confusion in the Christian Church concerning the Sabbath Day. The word which means "to desist from work" was set apart by the Hebrews on the seventh day as distinctly different from the other six. It is one of the original 10 commandments in Exodus. Technically the people counted the time from sundown Friday to sundown Saturday as the Sabbath. The Lord was pretty serious about it for in Exodus 31: 14 he says: "you are to observe the Sabbath, for it is holy unto you. Everyone who profanes it shall surely be put to death." Yikes!! Fortunately I don't know anyone who carries out that OT command. It was an identification mark setting apart Israel from every other nation as no where are Gentiles told to keep the Sabbath.
When Jesus came along he was accusedof breaking the Sabbath because he and his disciples were gathering corn on that day and Jesus even healed people on that day!! The Lord's attitude was to free them from the legalism of the Sabbath which was only a means to an end and not the end itself.
In the history of the early church, the believers deliberately chose not to worship on Saturday but on Sunday. Acts 20:7 "on the first day of the week". In I Cor. 16: 1-2 Paul reminds them that when they gather for worship on the first day of the week, set aside a collection for the needy. The Apostle John in- Rev. 1:10 says that "I was in the spirit on the Lord's Day" not the Sabbath.
How did the early church make the decision to use this freedom in worship? There are two main reasons. First: it was a celebration of the Risen Lord - the Resurrection which changed everything. They were under a new covenant as explained so well in Galatians and Hebrews; a covenant not centered on the law but upon grace. It was centered not on a day of rest but a day of celebration - the Lord's Day. But there is a greater reason that that. Second: In Matt. 5:17 Jesus says that he is the fulfillment of the law. With the coming of Jesus, God established a new covenant of faith and love (a moral law) rather than rules about diet, rites, observances and feast days, and punishment for various crimes. In Hebrews 4 we are invited into a "Sabbath rest" in Christ. It is not a day of the week, it's a life centered in Christ. The work of redemption of Jesus is now finished - He is our spiritual resting place. The real Christian Sabbath is in Christ!