It would seem that when they were first called 'CHRISTIANS' it referred to Disciples (and Paul) who were 'SABBATH-Observers.....which of course has TOTALLY CHANGED today where it now refers to 'sunday-observers'.
It is NOT the WORD ''CHRISTIAN'' as first intended that was wrong but HOW PEOPLE have changed in their belief while still using the original name. Christians have been tricked into changing their God....that is what happened !
Christians understand that no one is to act as our judge in regard to food or drink or in respect to a festival or a new moon or a
Sabbath day—17 things which are a
mere shadow of what is to come; but the substance belongs to Christ.
The early Christians began to worship God on Sunday because the
first day of the week became associated with Christ's resurrection (Matthew 28:1-10; Luke 24:1; John 20:1; Revelation 1:10). We see from Acts 20:7 and I Corinthians 16:1-3 that the early Church gathered together on the first day of every week in order to "break bread," and also to take up a "collection for the saints."
*Nowhere in the New Testament is the Church commanded to gather together to worship on the Jewish seventh day Sabbath.
History records that the early Christians were worshipping on Sunday as far back as the first and second centuries A.D. For example:
"But every Lord's Day, gather yourselves together, and break bread, and give thanksgiving after having confessed your transgressions, so that your sacrifice may be pure." (Didache c. 80-140)
"No longer observing the Sabbath, but living in the observance of the Lord's Day." (Ignatius, c. 105) Ignatius here reveals that the “Lord’s Day” is separate from the Jewish Sabbath.
"I will make a beginning of the eighth day, that is, a beginning of another world. For that reason, also, we keep the eighth day with joyfulness, the day also on which Jesus rose again from the dead." (Barnabas c. 70-130)
"There was no need of circumcision before Abraham. Nor was there need of the observance of Sabbaths, or of feasts and sacrifices, before Moses. Accordingly, there is no more need of them now." (Justin Martyr c. 160)
"We do not follow the Jews in their peculiarities in regard to food nor in their sacred days." (Tertullian c. 197)
"Just as the abolition of fleshly circumcision and of the old Law is demonstrated as having been consummated at its specific times, so also the observance of the Sabbath is demonstrated to have been temporary." (Tertullian c. 197)
"On the day of our Lord's resurrection, which is the Lord's Day, you should meet more diligently, sending praise to God who made the universe by Jesus... On this day, there is the reading of the Prophets, the preaching of the Gospel, the oblation of the sacrifice, and the gift of the holy food." (Apostolic Constitutions, compiled c.390)
So the actual Sabbath day according to the Jews is sundown on our Friday to sundown on our Saturday.
Sabbath keeping [with all it's rules and regulations] was
part of a covenant with Israel that is not applicable to Christians under the New Covenant and the Sabbath day did not change from Saturday to Sunday.