The Sabbath Puzzle

I have come across the following little poser in an old book. I wonder how many readers will see the author's intended solution to the riddle. Christians the week's _first_ day for Sabbath hold; The Jews the _seventh_, as they did of old; The Turks the _sixth_, as we have oft been told. How can these three, in the same place and day, Have each his own true Sabbath? tell, I pray.