In the old testament the Sabbath day was first instituted at creation when God rested from His works on the seventh day.
So the Sabbath transcends the law as it was before the law, and continues after the law. (whether literal or spiritual)
When Moses received the 10 commandments, the Sabbath was instituted for the Israelites as a day they could do no work, a day of rest.
Their worship was a daily worship and sacrificial system of animal offerings along with feasts and remembrances.
At the time of Jesus and the Apostles there was a daily sacrificial system along with Rabbis meeting with and teaching people in the temple daily.
Along with a Sabbath rest.
After the resurrection, the Apostles continued to teach and meet daily in the temple. And they observed the Sabbath.
After the temple was destroyed and diaspora, the Jews observed the Sabbath as a day of rest, fellowship, and ritual observances with prescribed candles and prayers, ect.
It is not clear to me how Christians transitioned after the destruction of the temple, other than what was decided at the Jerusalem Council.
But it does seem that the Jerusalem church observed the law.
http://www.fogwhistle.ca/acts/evidence.html
After Constantine, Sunday was made the official day of Christian observance.
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Since the Bible is a history of the church, and the early Jerusalem Church is in transition, still keeping the law. it is difficult. The early church struggled to define the transition.
Also, they did not yet have a compiled New Testament, so their bible was the Hebrew scriptures.