Bob, I've got to admit that you're making a pretty good case for keeping the sabbath. To say otherwise would be less than honest.
Still though, I am not convinced that the observance of the sabbath is required under the New Testament of Jesus Christ. In Acts 15 the matter concerning Gentile Christians and the law (of which the 4th commandment is a part) is discussed.
Act 15:5 But there rose up certain of the sect of the Pharisees which believed, saying, That it was needful to circumcise them, and to command them to keep the law of Moses.
Even in this letter there is not found a "No, you don't have to be circumcised or keep the law". All the apostles say is that they had given no such commandment.
Act 15:24 Forasmuch as we have heard, that certain which went out from us have troubled you with words, subverting your souls, saying, Ye must be circumcised, and keep the law: to whom we gave no such commandment:
The teaching that Gentiles were required to keep the law (including the 4th commandment) is characterized by the apostles as "subverting your souls", and the apostles, who operated by the guidance of the Holy Spirit had not commanded it. If they had intended the Gentiles to observe the sabbath, might they have made an exception, or made mention of it in some way?
Certainly the other nine commandments represent principles which are applicable to men of all ages. These nine can all be found in the NT as well.
Yes, God sanctified the 7th day back in Genesis. But until the command was given from Mt. Sinai, there is no record of anyone under the Patriarchal dispensation observing it. God's sabbath was not made known until He made it known to Israel in Exodus 20.
Neh 9:13 Thou camest down also upon mount Sinai, and spakest with them from heaven, and gavest them right judgments, and true laws, good statutes and commandments:
Neh 9:14 And madest known unto them thy holy sabbath, and commandedst them precepts, statutes, and laws, by the hand of Moses thy servant:
The arguments in favor of keeping the sabbath by Barnes, Moody, and others (including yourself) are well presented and obviously the product of much thought. But we are mere men, after all, and though I can say "Amen" to many of their points, as well as yours, I remain in disagreement with you on this issue.
I do look forward to continued discussions, sir.