Not a simple question
should not be treated in a reductionistic way
1) The Sabbath was from creation and the only use of the word holy in genesis was regarding the 7th day
2) the New Testament uses the term the Lord's day to the 1st day when Jesus rose and the only communion celebration in the New Testament the apostles celebrated at church was on Sunday, Pentecost was on Sunday, offering collection was on Sunday... a change occurred with the resurrection For example, Apostle John was given the book of Revelation on the Lord's day (i.e. Sunday)
3) The Sabbath was broadened to mean in part resting in the work of Jesus on the cross by faith and used that way in the book of Hebrews
4) The book of Romans appeals to those who set one day above others and those who treat each day alike to cut each other slack and respect each other's conscience. "Who are you to judge the servant of another, to his own master he stands or falls and the Lord is able to make him stand' in concluding chapters of Romans .... which also says to cut the vegetarians some slack as well...
5) Isaiah chapters 54 - 66 , post Isaiah 53 has the servants songs and Sabbath language is still prominently used There is a 'priesthood of believers' in the New Testament where people walk before God keeping a good conscience and that may be different for one or another.
6) Christians are not justified by their works or fruits but by grace through faith but will express their love of God as a fruit various ways.