For in six days the Lord made heaven and earth, the sea, and all that in them is, and rested the seventh day; wherefore the Lord blessed the Sabbath day and hallowed it.
Ex. 20:11.
"The Sabbath is a memorial of what the Creator did during the first week of time.
He rested on the seventh day.
Here is the origin of the week.
The weekly cycle is not derived from anything in nature.
Months are suggested by the phases of the moon; years, by the returning seasons; but the week can be traced only to the six days of creation, and the seventh of rest."
James White