On 7 March 321, Constantine I decreed that Sunday (dies Solis) will be observed as the Roman day of rest [CJ3.12.2]:
- On the venerable day of the Sun let the magistrates and people residing in cities rest, and let all workshops be closed. In the country however persons engaged in agriculture may freely and lawfully continue their pursuits because it often happens that another day is not suitable for grain-sowing or vine planting; lest by neglecting the proper moment for such operations the bounty of heaven should be lost. [41]
Though some Christians use the decree in support of the move of the Sabbath day to Sunday, in fact the decree was in support of the worship of the Sun-God (see Sol Invictus). In any event, the decree did not apply to Christians or Jews. It was part of the Roman civil law and religion and not an edict of the Church.[citation needed]
Although this does not indicate a "change" of the Sabbath, it does favor a different day for rest, in the cities at least, over the Jewish Sabbath day. The dominant religions in the regions of the world where Christianity was developing were pagan, and in Rome, Mithraism, specifically the cult of Sol Invictus, had taken hold. Mithraism met on Sunday. Some[who?] theorize that, because the practice favored the Christian day by coincidence, it also helped the church to avoid implicit association with the Jews. Jews were being persecuted routinely at this time, because of the Jewish-Roman Wars, and for this reason Constantine's edict, and Christian reception of it, is sometimes labelled anti-semitic. On a closely related issue, the Quartodeciman, Eusebius in Life of Constantine, Book III chapter 18, claims Constantine stated: "Let us then have nothing in common with the detestable Jewish crowd; for we have received from our Saviour a different way."
Source: http://en.wikipedia.org/wiki/Sabbath_in_Christianity
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