The Sfas Emes (5655) writes, "We really should strengthen ourselves on the final Shabbos of the year [to keep this Shabbos properly], as Chazal say, 'If the Jewish nation keep one Shabbos, they will be redeemed immediately,' and Chazal (Shabbos 12a) say that when we keep the Shabbos, שתרחם היא יכולה, this arouses Hashem's compassion on us."
The Yismach Yisrael ('א אות סוף י"נו) quotes earlier tzaddikim who compared this Shabbos to a long rod. When one lifts one end of the rod, the other end rises together with it. So, too, when one elevates himself and becomes close to Hashem on this Shabbos at the end of the year, it will elevate the entire year, and the upcoming year will be one of goodness and blessings.
Beis Aharon (129b) writes, "We speak about this all the time. The Shabbos before a yom tov is the preparation for the yom tov, as it states (in Kiddush) קודש למקראי תחילה, the Shabbos brings kedushah into the upcoming yom tov."
The Be'er Mayim Chaim (נצבים אתם) writes, "The origin of all the brachos and kindness that occurs to the individual, and to all people, throughout the week, is drawn from the Shabbos that precedes it. We understand from this that the awesome day of judgment for Klal Yisrael, the yom tov Rosh Hashanah, on which our lives and parnassah are decreed, is all decided and drawn from the Shabbos before it. Therefore, Shulchan Aruch (128:4) states that we always read parashas Nitzavim before Rosh Hashanah, because the word היום alludes to Rosh Hashanah (Zohar Pinchas 231a, and it states ַיּוֹםה נִצָּבִים אַת ֶּם). The concept that מרון כבני לפניו עוברים כולם, that all Yidden pass before Hashem in judgment" begins from this Shabbos. The clever will make use of this important day.
Rebbe Pinchas of Koritz zy'a said that at Shalosh seudos [of every week] it is decreed how the entire week will be for this person. (Imrei Pinchas 442). So, this Shabbos is a very important Shabbos for us, and in particular, the shalosh seudos of this Shabbos is essential. We gain so much from honoring the Shabbos properly.
The Baal HaTanya, quoting the Magid of Mezritch, said why we don't say החודש ברכת this week, that this is because Hashem, Himself, says החודש ברכת for this month. The החודש ברכת of every month receives its strength from the החודש ברכת of this week (from the Shabbos before Tishrei). (Tehillim Ohel Yosef Yitzchak, p.193).
Shalashudes and Humility
The Imrei Pinchas adds that Shalashudes is called אנפין דזעיר סעודה, "the seudah of the small face," a hint that one should be humble and consider himself small at this meal. Reb Shmerel of Vorchivker zt'l adds that shalashudes is an ideal time to daven to achieve humility. Therefore, on this Shabbos, one should daven that he be humble on Rosh Hashanah. As Chazal (26b) say that on Rosh Hashanah, feeling unworthy is helpful for the judgment.
