No, I don't find any moral obligation to keep the Sabbath day. It raises too many questions.DHK
Just a thought for you. By suggesting that we can not find a positive command in the NT to obey the 4th commandment, a type of reasoning seems to be set up to suggest that only that which is positively commanded in the NT is binding on the believer. You are correct that we do not find an explicit statement in the NT to "Keep the Sabbath" or other such language. Neither do we find a commandment to not engage in bestiality or to marry our sisters. And it is sad to report that some who have followed the aforementioned line of reason have espoused incest!
While the holy Law of God is not that which justifies a sinner or even sanctifies a sinner, it is holy, just, true and good for the believer in Jesus today and until the end of the age. I find it completely agreeable with the Scriptures as a whole that the 10 commandments are as binding on Christians morally as ever, and they will be forever. It is as immoral to break the 1st commandment today as it was the day it was given to Moses or for that matter as it was to Adam.
As someone who once argued against the perpetuity of the Sabbath day, it was looking at the whole of the 10 commandments and realizing that I could not wrestle one out over another. I could not in good conscience or reason suggest that it is still wrong for Christians to commit murder and still applies today and then suggest we are not morally obligated to the 4th commandment.
What does it mean "to keep the Sabbath Day"?
If one follows the OT injunctions, as some Messianic Jews do to this day, they would not drive their cars, use electricity, natural gas, gasoline, etc. They would not use anything that would be work or cause work for anyone else. The night before they would light their place of worship with candles and without the use of matches keep the candles lit for the remaining 24 hours or as long as they think they would need light until the Sabbath was over. Even to strike a match is considered work.
Where does one get the idea that "keeping the Sabbath" is just showing up for church on Sunday?
It is the sign of the covenant given to the Israelites and them alone.
Exodus 31:15 Six days may work be done; but in the seventh is the sabbath of rest, holy to the LORD: whosoever doeth any work in the sabbath day, he shall surely be put to death.
16 Wherefore the children of Israel shall keep the sabbath, to observe the sabbath throughout their generations, for a perpetual covenant.
17 It is a sign between me and the children of Israel for ever: for in six days the LORD made heaven and earth, and on the seventh day he rested, and was refreshed.
It is also evident that it is a day of rest that could only be kept in a geographical location such as the nation of Israel lived. I live in Canada, in fact in northern Canada. I could never adhere to the strict prohibitions of the Israelites. We would freeze when temperatures approach minus 70 F.
Consider a ten hour drive north of here. In the summer the sun never sets. In the winter the sun never rises. It is called the land of the midnight sun. How does one celebrate the Sabbath in a place where there is no sunset or sunrise for a good part of the year?
The principle in Creation, that God rested the seventh day, is just that--a principle of rest. Man should have one day out of seven to rest. Typically we do that in conjunction with what we call "The Lord's Day. But it is a day of rest. In our society keeping the Sabbath would not be a day of rest.