The Sabbath is "holy to the LORD." This is not something that men dreamed up. God does not say it is holy to certain denominations or certain people. It is holy to the Lord—set apart or sanctified to Him. He Himself sanctified it, as it says right in the commandment.
God, right in this covenant, sets how long it is to be observed or adhered to: as long as there are generations of Israelites. Are the generations of Israelites continuing? Yes, indeed. The generations continue, and therefore this covenant continues.
He also says that the Sabbath and its roots go back to Creation. He takes the Sabbath back to Genesis 2, not Exodus 16. This is significant. God places the beginning of the Sabbath at Creation to confirm that a physical or spiritual Israelite's relationship is with the Creator. The events of Exodus 16 were only a reminder of what already existed from the seventh day of Creation.