If you read through the Gospels, Christ only gave nine of the ten commandments to His followers: the commandment of the Sabbath was never reiterated.
This is true. However, if a person were to take that approach to the Gospels then that person must follow that line of reasoning to its logical conclusion.
The Gospels do not forbid homosexuality, bestiality, marriage to your father/mother or brother/sister, cannibalism, human sacrifice, or any other number of horrendous and unthinkable acts.
Surely they would not claim that, because the Gospels are silent on these matters, they must now be permitted, would they?
The Gospels also make it clear that Messiah did not come to loosen, eliminate, or annul any of the commandments. He made them more difficult!
"You have heard that the ancients were told, 'YOU SHALL NOT COMMIT MURDER' and 'Whoever commits murder shall be liable to the court.' But I say to you that everyone who is angry with his brother shall be guilty before the court; and whoever says to his brother, 'You good-for-nothing,' shall be guilty before the supreme court; and whoever says, 'You fool,' shall be guilty enough to go into the fiery hell." (Matthew 5:21-22)
"You have heard that it was said, 'YOU SHALL NOT COMMIT ADULTERY'; but I say to you that everyone who looks at a woman with lust for her has already committed adultery with her in his heart. (Matthew 5:27-28)
As far as the Sabbath, itself, here are a few facts that the anti-Sabbath crowd has to deal with:
1) The Sabbath was instituted by God on the seventh day of creation, not 1,500 years later at Sinai.
Thus the heavens and the earth were completed, and all their hosts. By the seventh day God completed His work which He had done, and He rested on the seventh day from all His work which He had done. Then God blessed the seventh day and sanctified it, because in it He rested from all His work which God had created and made. (Genesis 2:1-3)
2) The Sabbath was given to Israel in the wilderness (Exodus 16:22-26) at least two weeks before they arrived at Mt. Sinai (Exodus 19) and the commandments were given (Exodus 20).
3) When Messiah returns and rules over all the Earth, all mankind will come and bow down to Him from Sabbath to Sabbath (Isaiah 66:23).
There remains a Sabbath rest for the people of God. (Hebrews 4:9)