How do you keep the Sabbath?  This is a complicated question with a variety of answers.  The importance of taking one day a week for God cannot be overstated, but how, can fill multiple sermons.  What is considered man-make laws (i.e. the NT Pharisees) that Jesus criticized and what is following the 4th commandment is a fine line many times.  And I think often times this is a law that God looks at the heart much of the time.  And I think this is where Romans 14:5 comes into play.  “Each of you should be fully convinced in their own mind” how to follow this law.  And so you need to examine your own life to see how God wants you to obey this law and it might look a bit different for different people.  If God wants you to treat Sunday as sacred and a day of rest, than do it.  If another day is better for you to spend time with God, do that.  You also need to understand how Paul concludes this section about the “grey areas” like the Sabbath rest, “Everything that does not come from faith is sin.” (Rom 14:23). Let the Spirit speak to you on how exactly to obey, then do it, or you will be sinning.