The Sabbath is God's day of rest, not a day of rest of the Jews only, it is not owned by the Jews. It was kept by many before the Jews even existed. It was kept by all of Israel, until they sinned. Then God punished Israel for breaking His Sabbath, not just the Jews.
At the time of Christ, the Sabbath was still being observed by the Jews, and by Christ. Christ set the example. He did not keep the Sabbath because He was a Jew, but because He created it and understood the significance and meaning of the Sabbath.
It was made for man, not for Jews alone, nor for Israel alone. It is for all of us, and as followers of Christ, it is our duty to observe the day of rest that Christ created and observed.
Sunday is the first day of the week, and although we can worship God on that day, just as we can worship God on any of the week, it is on the Sabbath that we cease from our labours and have fellowship with God the Father and Christ. The Father is not accessible to those who do not seek Him on the Sabbath.
