The hebrew's sabbath we all know is saturday, that was changed when Our Lord Jesus's resurrection occurred on sunday.  So the new church decided that their new sabbath would be on the first day of the week or sunday to show that they differed from the old laws in a sort of rebellion against those who had conjured the death of the Messiah.  It was essentially brought about by St. Peter and the Apostles, from then on WHO is Christian celebrates the sabbath on sunday.  Andrea