God created the Sabbath, through Christ, at the beginning of creation (Genesis 2:2) in the old testament, which is also the inspired word of God.
Jesus said:
Mar 2:27 And he said unto them, The sabbath was made for man, and not man for the sabbath.
The word translated "man" in this verse is the greek word:
444 anthropos anth'-ro-pos
from 435 and ops (the countenance; from 3700); man-faced, i.e. a human being:--certain, man.
It was created for all human beings else the Lord God Jesus Christ would surely have specified "it was made for the Jews", or "was made for Israel".
Since it was created by God in the old testament, affirmed by God in the New Testament, and kept by God in the flesh in the New Testament, I feel that I have no choice but to obey God.
The Law was shadow, Christ is the substance. Now is you want to keep the Sabbath that is up to you, however, you best remember the admonition of Paul to those who wanted to put Christians under the Law, if you place yourself under any law of the Old Covenant you must continue to keep all of the Law. (see Galatians 5:3) Is that what you are advocating????