In the book of Exodus, the fourth commandment says to remember this day
Exodus 19Exodus... [DOC] [TLE] Remember the Sabbath Day to Keep It Holy | Desiring God [PAR] Oct 6, 1985 ... Fourth, no fudging on the commandment by saying, "Well, I will keep it, but I ... 
and Exodus 20:11 say that God "blessed" and "hallowed" the rest day.