In an email I was asked why Christians call Sunday the Sabbath when clearly it is Saturday in the bible.
In the very early days of the church the followers of Jesus were all Hebrews. As such they followed the tenants of Jewish worship. For the Hebrew people of Jesus day Sabbath began at sundown on Friday and lasted until sundown on Saturday. Most worship was done in the home or synagogue on Saturday.
For Hebrew Disciples of Jesus they would fulfill their worship as Jews on the Saturday Sabbath. Then at dawn on the first day of the week they would gather to celebrate the Resurrection of Jesus and this became known as "The Lord's Day.". At this worship the Gospel was preached, prayers said, new believers baptized and communion celebrated. As Sunday was a work day they then would go off to work.
Later when Gentiles, non-Jews, joined the growing ranks of the Disciples of Christ they would forgo the Hebrew worship and only attend the Sunday gathering at dawn to celebrate the resurrection. As the percentage of gentile Christians increased First Day or “Lord’s Day” worship became the most common form of Christian practice. Later Christians would begin calling Sunday the Sabbath even though that was not strictly true.
Today most Christians but not all practice Christian worship on the first day of the week to celebrate the Resurrection of Jesus the Christ. I do every Sunday.