Most people have heard of the 7th Day Sabbath. It is a day of rest on the 7th day.

Six days you will work, and you will do all your work. But the seventh day is a Sabbath for Yahweh your Elohim; you will not do any work—you or your son or your daughter, your male slave or your female slave, or your animal, or your alien who is in your gates— because in six days Yahweh made the heavens and the earth, the sea and all that is in them, and on the seventh day he rested. Therefore Yahweh blessed the seventh day and consecrated it. Exodus 20:9-11

Notice that this verse in Exodus refers back to the creation week. Sabbath day wasn't created in the desert of Sinai, but in the garden at creation:

And on the seventh day Elohim ended his work which he had made; and he rested on the seventh day from all his work which he had made. And Elohim blessed the seventh day, and sanctified it: because that in it he had rested from all his work which Elohim created and made. Genesis 2:2-3

Some people claim that the seventh day rest in the garden was a one time event, rather than a cyclical weekly celebration. If that were true, what would be the purpose of sanctifying and consecrating a day which would never be seen again? No, this day fits the pattern of a pause in the 7th cycle of the weekly period. There is significant disagreement about when the 7th day occurs, but that will not be addressed in this study (see Yahweh Created Time). The only comment here is that if Yahweh sanctified and consecrated a CERTAIN day, no other, different day will do. Yahweh doesn't change (Malachi 3:6), but if He DID, we would need scriptural evidence that He UNsanctifed His Holy day and sanctified (made Holy) a different day. This scripture doesn't exist.

The important thing is, Yahweh CONSECRATED (hallowed, made Holy) the seventh day. Is it even possible to unconsecrate something Holy? Once it is blessed and hallowed, who is man to try to make it common or ignored? Can man make a new calendar and choose a different (unholy, secular) day and make it Holy?

This is the "Seventh Day Sabbath" - the Holy Sabbath Day.