Question: Why do we celebrate Sunday as the Sabbath, when it was falsely changed from Saturday by Constantine?
Response:The seventh day of the week, Saturday, was and will always be the Sabbath. Constantine had no authority to change it. Sunday is not the Sabbath.
Constantine, a sun worshiper, is given credit for causing Christians to worship on Sunday instead of Saturday. Not true! Christians met on Sunday from the very beginning. Although the disciples went into the synagogue on the Saturday Sabbath to preach the gospel, it was on the "first day of the week [Sunday], when the disciples came together to break bread [i.e., for communion]" (Acts:20:7). It was also "the first day of the week" that they had the "collection for the saints" (1 Cor:16:1,2), further evidence of when they came together to worship the Lord.
We meet on Sunday for the same reason: it is the day Christ rose as the firstborn from the dead (Col:1:18), the "last Adam" (1 Cor:15:45), the progenitor of a new race of born-again believers.
The Sabbath was the day God rested from creating this temporal universe. We are in a new eternal creation where "all things are become new" (2 Cor:5:17). Our rest is Christ (Heb 3,4), not the Sabbath. We have dealt with this question in depth in the past. (See TBC for May '99, Nov '04, May '05.)