Did you notice that? "No manner of work. . ." "Cut off from his people. . ." "I will destroy. . ." No manner of work whatsoever could be done on the Day of Atonement, and death and destruction awaited those who would not keep this as it was commanded. And because of the severe punishment that awaited those who broke this commandment, God wanted to be very sure that people understood (1) when it began and (2) when it ended.