I agree with all of those, but I would like to add one more reason for keeping the Sabbath. We usually think of it as separate from the annual feasts, such as Passover and the Feast of Tabernacles, but it is found in the same lists, for example in Leviticus 23. As with all the other feasts, the Sabbath both looks back to commemorate an event that has already happened and looks forward to some part of God's redemptive plan. For example, Passover commemorates the Exodus from Egypt and points forward (or what was then forward) to Christ's crucifixion. The Sabbath is no different in this respect. It looks back to commemorate the creation, and looks forward to our final rest when Christ returns. Some people say that the entire week is prophetic. The Bible says that a day is as a thousand years with the Lord and a thousand years as a day. All of human history, from the creation until Christ's return (or the Messianic Kingdom, as the Jews put it) will be 6000 years (6 days), and then the millennial reign of Christ will come (the seventh or Sabbath day).
The TOG