The Sabbath day was given as a sign for Israel (Eze.20:12) and is not repeated in the commandments as restated by Paul in Romans 13.
Moreover in Romans 14:6 he writes, One man esteemeth one day above another; another esteemeth every day alike; let every man be fully persuaded in his own mind
Yah, but then why did God create it at the beginning?
Gen 2:2 And on the seventh day God ended His work which He had made. And He rested on the seventh day from all His work which He had made.
Gen 2:3 And God blessed the seventh day and sanctified it, because in it He had rested from all His work which God created to make.
Since it was blessed and sanctified (set apart) at the beginning, long before Israel, a literal interpetation of the bible would indicate that it's still blessed and sanctified because it was never deblessed or desanctified by God.
Moreover in Romans 14:6 he writes, One man esteemeth one day above another; another esteemeth every day alike; let every man be fully persuaded in his own mind
Paul never mentions the sabbath in that verse or the chapter. In context, the whole chapter is about eating and drinking. What Paul is probably referring to is fasting. Some jews at the time thought they were holier than others cause they fasted on certain days of the week that others didn't. This is made clear in the next verse:
Rom 14:6 He who regards the day regards it to the Lord; and he not regarding the day, does not regard it to the Lord. He who eats, eats to the Lord, for he gives God thanks; and he who does not eat, does not eat to the Lord, and gives God thanks.