As Israel Travelled As Israel travelled ; prior to their arrival at Sinai (and receiving the law on tablets of stone); we read in Exodus 16:2 "the Lord hath said , tomorrow is the rest of the holy SABBATH unto Yehovah.” In verse 28 “And Yehovah said unto Moses, How long refuse ye to keep my commandments and my laws?” Elohim's commandments had been violated and refused for many generations, not just for a few days prior ,or he would not have been able to make this statement.
Elohim had called his (peculiar) people apart,
(For thou art an set apart people unto Yehovah thy Elohim, and Yehovah hath chosen thee to be a peculiar people unto himself, above all the nations that are upon the earth.Deut.14:2) and now back to their land; and the first priority of all the commandments was the keeping of the SABBATH. Again in Exodus 16:29 "See, for that Yehovah hath given you the Sabbath, therefore he giveth you on the sixth day the bread of two days; abide ye every man in his place, let no man go out of his place on the seventh day". This happened before the Commandments were issued. Some may think that any day will satisfy Elohim, but YHWH left no doubt about the day he wanted observed, he told and showed Israel exactly which day was the Sabbath. For 40 years (over 2000 weeks) a double portion of manna fell on the sixth day, and no manna fell on the Sabbath, until Israel entered the promised land (Exodus 16:35, Joshua 5:12). 
At Mount Sinai
True Believers
On the way to the garden
The "Lord's" Day
The SABBATH continues
Lo this I have found
Always the Scriptures reaffirm
information link about Red Sea crossing point
red sea crossing point