Commentaries:
Consider the import of what Paul says here. He is to be a light to the Gentiles, showing them the way. What day did he appoint to meet with these people? He had a wonderful opportunity at the end of that first Sabbath, which broke up in a dispute, to tell the people: "Now, wait a minute. Yes, I want you to all come back, but why not just do it tomorrow, on Sunday?" Instead, in order to continue in the grace of God, he had them wait a full week. Then, on the Sabbath, they assembled again. Note that this occurs in the general area of Galatia.
John W. Ritenbaugh
The Covenants, Grace, and Law (Part Twenty-Four)
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