God gave man His Sabbath to keep mankind in the right knowledge and proper worship of the true God. But how does the Sabbath identify God? How does it point to the true God, rather than a false one? Would not Sunday work just as well?
Notice Exodus 31:17: "It is a sign between Me and the children of Israel forever; for in six days the Lord made the heavens and the earth, and on the seventh day He rested and was refreshed." God rested from the work of creation on the seventh day of creation week. Not on Sunday, the first day of the week—only the seventh day of the week points back to Creation.
Creation is the proof of God's existence. The act of creating identifies the Creator. God set aside as holy the only day that is a memorial of the act of creating. He appropriated the only day that points, constantly, every seventh day of the week, to the existence of the Creator.
God set that particular day apart from others as His day. He made that particular day sacred and holy to Him, designating it as the very day on which He commands His people to assemble for worship. It is the day man is commanded to rest from his own work and activities, and to be refreshed by assembling with other obedient worshippers in spiritual fellowship.
No other day is a memorial and reminder of the original creation. True, Satan has deceived this world into supposing Christ's resurrection occurred on Sunday morning at sunrise—the very time that has always been the time of pagan sun-worship. The truth is, however, that the resurrection of Jesus Christ actually occurred on the Sabbath, not on Sunday! Additionally, nowhere in the Bible does God tell us to celebrate the day of Christ's resurrection. Instead, Christ tells us to celebrate His death through the observance of Passover (I Corinthians 11:23-26).
So here we find a main purpose in the Sabbath: It identifies God! The very day which God set aside for assembly and worship points as a memorial to whom we are to worship—the Creator and Ruler of all that exists!
The Sabbath also was given as a sign that identifies who the people of God are. Not only does this special covenant say, "that you may know that I am the Lord," but it also says, "that you may know that I am the Lord who sanctifies you" (Exodus 31:13).
Sanctify means "to set apart for holy use or purpose." On the seventh day of creation week, God sanctified the Sabbath day—He set it apart for holy use. By adding the phrase "who sanctifies you," God says the Sabbath is a sign that He also sanctifies those who are His people. He sets them apart from other people as His, for His holy purpose.
So the Sabbath identifies both who God is and who God's people are!