" a day given only to the Israelites"

Still sticking with that mantra, eh, Elaine?  As you very well know, the day was set apart and made holy long before there was an Israelite.  To maintain that it was never kept by anyone until the Exodus, is to argue from silence.  And it can't be proven.  Jesus, our Example, who kept the day Himself, was clear about the day being made for man, not just for Jews.