In a shmuess to talmidim, Rav Moshe Shternbuch, gaavad of the Eidah Hachareidis, discussed the topic of Rosh Hashanah coinciding with Shabbos. He cited the words of the Chasam Sofer, who asserted that in a year when the shofar is not sounded on the first day of Rosh Hashanah due to it being Shabbos, the merit of observing Shabbos properly serves as a protective shield for Klal Yisroel in place of the shofar.
Furthermore, Rav Shternbuch quoted the Aruch Laner, who noted that in years when Rosh Hashanah falls on Shabbos, the outcome for Klal Yisroel can go one of two ways: either it can be a particularly auspicious year, akin to the one when the sin of the Eigel was forgiven, the Mishkan was established, and the entry into Eretz Yisroel occurred, or, chalilah, it can lead to calamity, as seen in the destructions of both Botei Mikdosh, which took place when Rosh Hashanah coincided with Shabbos.
The reasoning behind this, as elucidated by the Aruch Laner, lies in the fact that in such years, when the shofar is not sounded, we rely on the observance of Shabbos as a sign of our commitment. If Klal Yisroel faithfully observe Shabbos as they should, then Shabbos itself becomes a source of shemirah, protection, for them. However, if they neglect the proper observance of Shabbos, they forfeit this safeguard, and the accusers against them are not silenced.
Rav Shternbuch concluded his message with guidance for the upcoming year: “Therefore, in this year, it is advisable to accept upon ourselves a kabbolah regarding kavod Shabbos. This may include consistently studying the halachos of Shabbos throughout the entire year, sanctifying the Shabbos through limud haTorah, or encouraging others to fulfill their obligation of learning hilchos Shabbos and becoming proficient in them. These efforts will ensure that the sanctity of Shabbos protects us and silences the accusers.”
{Matzav.com Israel}