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????
There is ample evidence. God created the sabbath in Genesis:
Gen 2:2 On the seventh day God finished his work which he had made; and he rested on the seventh day from all his work which he had made.
Gen 2:3 God blessed the seventh day, and made it holy, because he rested in it from all his work which he had created and made.
It's creation far predates the covenent affirmed at Mount Sinai.
Also God says in Genesis about Abraham:
Gen 26:5 because Abraham obeyed my voice, and kept my charge, my commandments, my statutes, and my laws."
This indicates that certain commandments, statutes and laws were known to some people in Abrahams time, centuries before Sinai. It's not inconcievable that the Sabbath was one of them.
Also God was commanding his people to keep the sabbath before the old convenent was instituted:
Exo 16:23 He said to them, "This is that which Yahweh has spoken, 'Tomorrow is a solemn rest, a holy Sabbath to Yahweh. Bake that which you want to bake, and boil that which you want to boil; and all that remains over lay up for yourselves to be kept until the morning."
This occurs days, if not weeks, before the covenent was struck at Sinai.
In addition, the sabbath is so special to God that he seems to have designated a seperate covenent for it and it alone:
Exo 31:16 Therefore the children of Israel shall keep the Sabbath, to observe the Sabbath throughout their generations, for a perpetual covenant.
Either way the sabbath clearly pre-dates the covenent agreement made at Mount Sinai.
There is no New Testament commandment given to continue to observe the Sabbath. (see Acts 15 - surely the Council of Jerusalem would have mentioned the need to keep the Sabbath when instructing the Gentile converts.)
The gentiles weren't instructed not to kill and rob so does that make it okay? Besides, gentiles did keep the sabbath:
Act 13:42 So when the Jews went out of the synagogue, the Gentiles begged that these words might be preached to them the next Sabbath.
Act 13:44 The next Sabbath almost the whole city was gathered together to hear the word of God.
Act 18:4 He reasoned in the synagogue every Sabbath, and persuaded Jews and Greeks.
Everyone was keeping the sabbath.
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????
Christ is the substance. Christ kept the law, including the sabbath. When we let the spirit of Christ live in us, it is easy to do what Christ did because the love of Christ works in us. It's in that sense that the law is written in the hearts of Christians, it hasn't disappeared, but has been fulfillled with the spirit of Christ.