Did you even read Romans 14?
The context of the whole chapter of Romans 14 from beginning to end has to do with regard to food practices. "Paul is writing about asceticism. Some in the church at Rome believed Christians should eat only vegetables. Paul calls these people 'weak in the faith' (verses 1-2. The stronger in the faith knew they could also eat meat. Nothing in God's law prescribes vegetarianism. The stronger in faith knew they were free from non-biblical asceticism.
A part of the controversy that had sprung up between the weak and the strong Christians was the esteeming of days. In Rome some people had the pagan idea that on certain days certain foods should or should not be eaten. In this whole chapter Paul was just showing that others should not be offended, particularly weak members who have not yet learned the truth about the proper Christian diet and that they should not be judged by the the stronger in the faith." Nothing in the chapter is said with regard to the Sabbath or the first day of the week.
Hasting's Encyclopedia of Religion and Ethics.
"We assume, because we have been raised with an anti- Torah bias, that the text must be talking about Sabbath, but that is a pure assumption not required by the text. To say that the verse must mean, that if we are honoring the Sabbath as God commands numerous times and places throughout Scripture (not a gray area), that those who do so are weak in the faith, is an interpretation coming from an anti- Torah bias that has been imposed on the text, but which the text does not require."
A footnote in Calvin's Commentaries regarding verses 5-6: " It has been suggested as a question by some, whether the Christian Sabbath is included here? The very subject in hand proves that it is not."
Expositor's Greek Testament with regard to verse 5:"It is not probable that there is any reference...to the Jewish Sabbath..."