The Bris Avrohom of Slonim would say: Since Chazal write, “One day of the year can be considered like the complete year” (Rosh Hashanah 2b), it is possible for one to rehabilitate the entire year even on its final day. Certainly the same applies to the last Shabbos of the year: It is possible to elevate the Shabbosos of the entire year on this final Shabbos. His son in law, the Nesivos Shalom adds: Aside from the restoration of the past year that can be achieved on this final Shabbos, this Shabbos serves also as the gateway and preparation for the awesome Yomim Noraim of the following year