Another important facet of the Day of Atonement was that it was called a Sabbath of Sabbaths.
It shall be a sabbath of rest [Hebrew—a Sabbath of sabbatism, a rest of rests] unto you, and ye shall afflict your souls, by a statute for ever.
This emphatic description for a day of rest is only used of the weekly Sabbath, the Sabbath year, and the Day of Atonement. Other holy days were Sabbaths, days of rest; but these were special. They were the Sabbath of Sabbaths.