It is well documented that the emperor Constantine made it illegal for "Christians" to observe the Sabbath, because he didn't want them to practice the same worship as the Jews.
I believe that Jesus observed every Sabbath as well as every Feast of the Lord, and even Paul made sacrifices in the Jewish temple on the Sabbath. Why do Catholics prefer to follow the decrees of a pagan emporor, rather than to do as Jesus did and keep the Sabbath Holy?
The Lord's Day didn't originate with Constantine. Sunday is referred to in Scripture as "the first day of the week," since Saturday, the Hebrew sabbath, was the "last day of the week."
Acts 20:7 - this text shows the apostolic tradition of gathering together to celebrate the Eucharist on Sunday, the "first day of the week." Luke documents the principle worship was on Sunday because this was one of the departures from the Jewish form of worship.The "Lord's Day," Sunday, has been different from the Jewish sabbath from the earliest times:1 Cor. 16:2 - Paul instructs the Corinthians to make contributions to the churches "on the first day of the week," which is Sunday. This is because the primary day of Christian worship is Sunday.
On the Lord's own day, assemble in common to break bread and offer thanks, but first confess your sins so that your sacrifice may be pure." Didache, 14 (A.D. 90)."If, therefore, those who were brought up in the ancient order of things have come to the possession of a new hope, no longer observing the Sabbath, but living in the observance of the Lord's Day, on which also our life has sprung up again by Him and by His death--whom some deny, by which mystery we have obtained faith, and therefore endure, that we may be found the disciples of Jesus Christ, our only Master." Ignatius, To the Magnesians, 9:1 (A.D. 110).