Answer: We have all been taught to believe that the Council of Laodicea, Canon 29 stated: Christians shall not Judaize and be idle on Saturday, but shall work on that day; but the Lord’s Day they shall especially honor, and, as being Christians, shall, if possible, do no work on that day. If however, they are found Judaizing, they shall be shut out from Christ.
According to Karl J. von Hefele, a Catholic bishop, in his History of the Councils of the Church from the Original Documents, states that the word “Saturday” (dies Saturni) does not exist either in the Greek or Latin text. Rather, the word “Saturday” was supplied in the English translation in place of the word Sabbato, meaning Sabbath.
Quod non oportet Christianos Judaizere et otiare in Sabbato, sed operari in eodem die. Preferentes autem in veneratione Dominicum Diem si vacre voluerint, ut Christiani hoc faciat; quod si reperti fuerint Judaizere Anathema sint a Christo.
At the time the Julian calendar was being enforced upon Christians for religious purposes, no one confused the word Sabbato with dies Saturni. Simply everyone at that time knew these were names for two different days on two distinctly different calendar systems. It is only as the facts of history have been forgotten, that Saturday has been assumed to be the seventh-day Sabbath of Scripture.