WHY ARE WE TO CELEBRATE THE SABBATH?

Exodus 20:11  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. (KJV) Deuteronomy 5:15  And remember that thou wast a servant in the land of Egypt, and that the LORD thy God brought thee out thence through a mighty hand and by a stretched out arm: therefore the LORD thy God commanded thee to keep the sabbath day. (KJV)

Note: The assumption of contradiction is that Exodus is telling us that we celebrate the sabbath because God rested on the seventh day, and that Deuteronomy is telling us that we celebrate it because God delivered the Israelites from Egypt. Obviously, both are true.  We celebrate on the seventh day (as opposed to the fifth or sixth) because God rested on the seventh day, but our reason for celebrating it is that God delivered the Israelites from Egypt.  Not a contradiction.