Like the Sabbath, the week originated at creation, and it has been preserved and brought down to us through Bible history. God Himself measured off the first week as a sample for successive weeks to the close of time. Like every other, it consisted of seven literal days. Six days were employed in the work of creation; upon the seventh, God rested, and He then blessed this day and set it apart as a day of rest for man.
But the assumption that the events of the first week required thousands upon thousands of years, strikes directly at the foundation of the fourth commandment. It represents the Creator as commanding men to observe the week of literal days in commemoration of vast, indefinite periods. This is unlike His method of dealing with His creatures. It makes indefinite and obscure that which He has made very plain.
 

The importance of the Sabbath as the memorial of creation is that it keeps ever present the true reason why worship is due to God"--because He is the Creator, and we are His creatures. The Sabbath therefore lies at the very foundation of divine worship!

Had the Sabbath been universally kept, man's thoughts and affections would have been led to the Creator as the object of reverence and worship, and there would never have been an idolater, an atheist, or an infidel.
The keeping of the Sabbath is a sign of loyalty to the true God, "Him that made heaven, and earth, and the sea, and the fountains of waters."  Rev. 14:7