Commentaries:
Christ set the Sabbath-keeping example for his apostles, and Paul, following His example, tells us we are to imitate him as he imitates Christ (I Corinthians 11:1). Paul preached to the Jews and Gentiles on the Sabbath because the Sabbath is for everyone, not just the Jews. These Gentiles were keeping the Sabbath in the synagogue with the Jews on the seventh day, not Sunday.
Martin G. Collins
The Fourth Commandment