Pope Sylvester turned the switch

For the mystery of iniquity doth already work: 

2 Timothy 2:7

"From the earliest times, the first day of the week, in the religion of idolatry, was dedicated to the worship of the sun; so that when Christianity come into contact with that false system, Sunday was a venerable day throughout all the heathen world.

Constantine's law, it will be noticed, speaks not of the lord's day, or the Christian Sabbath, but of "the venerable day of the sun." 

This was the heathen, not the Christian, name of the day. 

And this law was on behalf of Sunday as a heathen, not a Christian, institution. 

The law was dated A.D. 321. Constantine did not experience his so-called conversion to Christianity till A.D. 323, two years afterward. The day following his Sunday law, he enacted another, regulating the work of the soothsayers who foretold future events by examining the entrails of beasts offered in sacrifice to the gods; fitting companion to the preceding. 

Q: But how did this heathen law come to have a bearing upon Sunday as a Christian observance? 

A: The pope of Rome cheerfully looked after that matter. 

When Constantine professed Christianity, his sunday law was left on the statute book unrepealed; and Sylvester, bishop of Rome, since

called pope, took advantage of this fact; and giving the day the imposing title of Lord's day, by his apostolic authority, enforced it upon the church as a Christian institution. 

Constantine also, then deeming himself as much the head of the church as the pope, took upon himself to elevate it still further, by church authority, as a Christian observance, taking "upon him," says Heylyn, not only "to command the day, but also to prescribe the service."

In the days of Constantine so near had the two systems come together that it was not difficult to transfer institutions from one to the other. 

Sunday had heretofore run on the pagan track; now it could be switched off upon the Christian. 

Pope Sylvester turned the switch; 

and henceforth Sunday is a palace sleeping car 

upon the Christian track, 

and not upon the heathen. " 

Uriah Smith