"Exo_20:8.Remember the Sabbath-day.
The object of this Commandment is that believers should exercise themselves in the worship of God; .......we must remember the 
spiritual substance of the type; for not only did God prescribe certain days for the holding of assemblies, in which the people might give attention to sacrifices, prayers, and the celebration of His praise; but He placed before their eyes as the perfection of sanctity that they should all cease from their works.
Remember the Sabbath-day. The word keep is used in Deuteronomy with the same meaning.
Hence we infer that it is no trifling matter here in question, since God enforces the sanctity of the Sabbath by these two words."
JohnCalvin