By church law updating
This idea originated in the 19th century within Seventh-day Adventism (which regards the Sabbath as Saturday), and some on the fringes of the SDA church have taken a handful of failed Congressional bills and papal writings and inflated them into the trigger of the apocalypse.
This is quite ironic considering that you would think that opposition to blue laws might come from more secular groups.
[…] he claims to have changed the Sabbath to Sunday, and commands all to hallow the day which he has blessed.
He declares that those who persist in keeping holy the seventh day are blaspheming his name by refusing to listen to his angels sent to them with light and truth." He also identifies the Number of the Beast from Revelation , 666, from the numerical values of the Pope's presumed title of "Vicarius Filii Dei"; actually, this has never been an official title of the Roman Pontiff.
In the later Middle Ages, the Church exerted a potent influence upon law.
A very extensive jurisdiction was exercised by the ecclesiastical courts, which not only secured a more general exemption of the clergy from secular jurisdiction, but extended their own jurisdiction over laymen.
In numerous instances, the origins go back to the early Middle Ages, that period which lies between the late fourth century and the end of the eleventh century; while some other precedents arose still earlier in the institutions of the Germanic and the Celtic peoples, or in the Greco-Roman civilization.
Consequently, the relations of religion and law in the early Middle Ages deserve much more attention than they have received in popular accounts.
But many of the above-mentioned respects in which the Church influenced secular law in the later Middle Ages owed their foundations to periods earlier than the twelfth and the thirteenth centuries.As was natural from the fact that marriage was considered a sacrament, the Church also exercised control over matrimonial cases and such related matters as the legitimacy of children, the recording of marriages and of baptisms, wills bequeathing personal property, and distribution of the property of intestates.For the exercise of its wide jurisdiction, the Church had developed courts superior to the secular courts in point of procedure, differentiation of penalties according to motives and other attendant circumstances, and use of the principles of jurisprudence.In international relations, it was principally the Church, which kept alive the conception that all Christian peoples constitute a society of Christian nations, later broadened into the idea of a society of civilized nations; and there were valuable ecclesiastical contributions to the modern conviction that foreigners have legal rights, even in the absence of a treaty to that effect.Ecclesiastics taught that Christian principles should be followed in settling controversies between Christian princes and peoples; arbitration by the Pope was resorted to in a number of cases; and the Church made efforts to lessen the brutality of war.