Romans 14:510
tells us that one man esteems one day of the week above another; another esteems every day alike. Then Scripture tells us that everyone should be fully persuaded in his own mind. We are not to judge each other regarding the day on which we worship.
Jesus did keep the Sabbath. He had to keep the whole Law to be the perfect sacrifice. The Bible makes it clear that the Law has been satisfied in Christ. The reason Paul went to the synagogue each Sabbath wasnt to keep the Law; that would have been contrary to everything he taught about being saved by grace alone (Ephesians 2:8,9). It was so he could preach the gospel to the Jews, as evident in the Book of Acts. Paul had an incredible evangelistic zeal for Israel to be saved (Romans 10:1). To the Jew he became as a Jew, that he might win the Jews (1 Corinthians 9:19,20). That meant he went to where they gathered on the day they gathered.