Fasting or Feasting?
In 321 AD, the Sabbath was changed from Saturday to Sunday.
This was prophesied.
And he shall speak great words against the most High, and shall wear out the saints of the most High, and think to change times and laws: and they shall be given into his hand until a time and times and the dividing of time.
- Daniel 7:25 (KJV)
The Sabbath commandment is the only commandment that is both law and time.
One strategy the Roman Catholic Church used for this, was to make Sunday more of a "feast" day, whereas the Sabbath was traditionally more of a "fast" day.
The other strategy had of course everything to do with the Sunday resurrection, which they said was now the new Sabbath.
There is not a single verse in the Bible to back that up of course. God's Law is eternal and never changes.
Remember the sabbath day, to keep it holy. Six days shalt thou labour, and do all thy work: But the seventh day is the sabbath of the Lord thy God: in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates: For in six days the Lord made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the Lord blessed the sabbath day, and hallowed it.
- Exodus 20:8-11 (KJV)
This is also the only commandment that starts with "Remember". Maybe God knew we would forget. 