666 is unholy, unholy, unholy the name of the Beast
and 777 is Holy, Holy, Holy Gods Seventh Day.

And in searching around on this issue the questions that comes to mind is..

Has the [Catholic] church power to make any alterations in the commandments of God?

To actually change a day that has been blessed and sanctified from creation? I would says No.
Nobody is above God.
And God called the Seventh Day Holy.
777 Holy, Holy, Holy thats Tri-Unity right there.
666 is the unholy tri-unity an imitation of Our God.
You can just see it right there.

And in searching around and looking into this issue the Proof Directory has some answers of why that shouldn't be so.

http://bible.proofdirectory.com/answers/92_gods_memorial.htm

And then again there is the mark and some believe the mark of the beast which will have to do with worship has to do with making a law that changes the Sabbath to the 8 day or 1st day of the week.
Then I looked into the Hebrew and found something interesting in why they may believe this to be true.
First in looking into it the church is trying to make a sunday law, it's true.
Which will only bring persecution to God's people as lot of them see the 7th day as the Holy day which it is.
And persecution to the Jews which honor the Sabbath 7th day.
So that makes one wonder? Why would they do it?