Yom Kippur is called Shabbos Shabbason-The head of all future Shabbosim:
Yom Kippur is called Shabbos Shabbason being that it is the Shabbos of all the Shabbosim of the year. This is because all the Shabbosim of the year are considered like a weekday in comparison to the Shabbos of Yom Kippur. A ray of Yom Kippur shines on every Shabbos.
 Likkutei Torah Haazinu 72b