Jesus was a Jew. Observed Friday sunset as the Sabbath with his disciples and followers. They went to the temple or a house, where teachings were taught. Jews and gentiles congregated together to learn of God.
After Revelation in the Bible and the death of the disciples. Doctrines, teachings, altered by man making traditions and his own interpolations. Sunday as a Sabbath day came along and took root.
The real Bible Sabbath as one who follows Jesus is Friday sunset. Today people who observe Sunday and shun the Bible Sabbath are in sin. Working, taking your own pleasure,and most of all not congregating on the real Bible Sabbath and making it a Holy Day.
It's like going through a red light[Friday sunset Sabbath] and then pulling over and parking [Sunday Sabbath]. Breaking the Sabbath Law and finding sin, for most unknowingly I think. OFFICER, I DIDN'T SEE THE RED LIGHT.