Shabbat Teshuvah has a special “plus” compared to the other Ten Days of Repentance. Each of the six weekdays of the Ten Days of Repentance affects one particular day of the week for the whole year (the Sunday corrects every Sunday of the past year and grants strength for every Sunday of the coming one; and so on). However, Shabbat of the Ten Days of Repentance affects not only every Shabbat, but every day of the past and coming year.

Why is this? Shabbat includes every day of the week: it creates an elevation and perfection in every day preceeding it, as Scripture states, “and the Heaven and Earth were completed,” and it also elicits a blessing for the days after it, as the Zohar explains, “from it are blessed all days.”6 Thus, since Shabbat Shuvah includes every Shabbat of the year, it influences all days of the year through them.

Moreover, Shabbat Shuvah has a “plus” even in relation to Rosh Hashanah and Yom Kippur. For the main elevation that Shabbat Shuvah accomplishes in the preceding days is for that week, meaning that Shabbat completes the service of Rosh Hashanah. Also, the blessing from this Shabbat for the days afterward pertains chiefly to its own following week: it blesses Yom Kippur.

(Sichat Shabbat Parshat Vayeilech 5746)