For most of my life, I’ve heard Christians refer to Sunday as “the Sabbath.” And for most of my life, I’ve never questioned the use of that term for Sunday. But I’ve come to believe that it is incorrect. I'll briefly explain why.
As is well known, in the first Genesis account of creation, the Sabbath refers to the seventh day, the last day of the week:
“Thus the heavens and the earth were finished, and all their multitude. And on the seventh day God finished the work that he had done, and he rested on the seventh day from all the work that he had done. So God blessed the seventh day and hallowed it, because on it God rested from all the work that he had done in creation” (Genesis 2:1-3 NRSV).
On the Jewish calendar, the seventh day is Saturday. Hence the rationale for Saturday synagogue worship.
Christianity retains this ordering of the week. Look at any liturgical calendar, and you’ll see that the last day of the week is Saturday and the first day of the week is Sunday (on the secular calendar, of course, the first day of the week is Monday).
Which brings us to the Christian day of worship. Because of its association with the resurrection of our Lord, Sunday became the focus of Christian worship. This is because Jesus was crucified on Friday, and was raised (as the Nicene Creed puts it) “on the third day.” And so every Sunday is a Feast Day of the Resurrection, even during Lent (if you include Sundays, there are 46 rather than 40 days during Lent). As such, it should not be confused with the Sabbath. Matthew, for example, makes the point very clearly when he describes how the women discovered Jesus’ empty tomb “After the sabbath, as the first day of the week was dawning …” (Matthew 28:1 NRSV; emphasis added).
The Book of Common Prayer reinforces what the New Testament teaches: that Sunday is not the Sabbath. Note, for example, the thematic focus of the Collect for Saturdays in the office of Morning Prayer (BCP, p. 99):
Almighty God, who after the creation of the world rested from all your works and sanctified a day of rest for all your creatures: Grant that we, putting away all earthly anxieties, may be duly prepared for the service of your sanctuary, and that our rest here upon earth may be a preparation for the eternal rest promised to your people in heaven; through Jesus Christ our Lord. Amen.
And note also the thematic focus of the Collect for Sundays in the office of Morning Prayer (BCP, p. 98):
O God, you make us glad with the weekly remembrance of the glorious resurrection of your Son our Lord: Give us this day such blessing through our worship of you, that the week to come may be spent in your favor; through Jesus Christ our Lord. Amen.
The Prayer Book differentiates Saturdays and Sundays because their theological meanings are quite different. So rather than calling Sunday the Sabbath, it is more theologically and liturgically accurate to call it “the Lord’s Day.” Confusing or conflating these two days, we lose the richness of their respective meanings and how we can and should observe them.