The story of the creation as narrated in Genesis follows a logical classification of beings created each day, ending finally when God rested on the seventh day, and for that reason "God blessed the seventh day and made it holy." (Gen.2:3). The narrative thus designedly places before the Jews a reason why the seventh day of the week should be regarded as 'the Lord's day', the Sabbath day (day of rest) and a holy day.

The Sabbath observance is included also in God's commandments: "Remember the Sabbath day and keep it holy. For six days you shall labour and do all your work, but the seventh day is a Sabbath for Yahweh your God. You shall do no work that day" (Exodus 20:8-10; Deut. 5:12-14).

The old dispensation was a preparation for the new. In the history of Christ, we see the completion, perfection and fulfillment of what had been forecast, foreshadowed and looked forward to in the history of the Jewish people. The creation was in fact a prelude to the new creation in the spiritual order which would be ushered in by the death and resurrection of Christ. Just as in the story of the creation God completed His work and rested on the seventh day, so in the new creation, the redemptive mission of Christ was completed by his death, followed by his resurrection.

God's resting on the seventh day was presented to the Jewish people as a congruent reason for keeping a day of the week holy. But now there was a cogent reason for keeping the Sabbath holy when Christ rose from the dead, which was the apex and the most convincing proof of the divine origin of his messianic mission.

But this event, the resurrection, took place not on the seventh day but on the eighth, that is, the first day of the Jewish week, which corresponds to our Sunday." After the Sabbath, and towards dawn on the first day of the week, Mary of Magdala and the other Mary went to visit the sepulchre." (Matthew 28:1. Cf also Mark 16:1-2; Luke 24:1; John 20:1).

The first day of the week therefore assumed a very special significance for the new dispensation, for the followers of Christ. They saw in the resurrection, greater reason to keep the first day if the week holy than the reason for keeping the seventh day holy. The first day of the Jewish week thus became the new, 'Lord's day' of the Christians. (Apoc. 1:10).

That is why, assemblies were held in the early Church were held on the first day of the week (our Sunday). "On the first day of the week we met to break bread." (Acts 20:7). "Every first day of the week, each of you must put aside what he can afford, so that collections need not be made after I have come." (1 Cor. 16:2).

From those early days the eighth day or first day of the Jewish week (instead of the last) became the Sabbath day, the Lord's day, of the Christians, and that for a reason they looked upon as weighty enough for the change.

Vatican II has this say on he Catholic practice: "By an apostolic tradition which took its origin from the very day of Christ's resurrection, the Church celebrates the paschal mystery every eighth day; with good reason this, then bears the name of the Lord's day or the day of the Lord." (Constitution on the sacred Liturgy, 106)

Those Christians, particularly the Seventh-Day Adventists and the Seventh-Day Baptists, who cling to Saturday as the Sabbath day, are still in Old Testament times!