We all know that the Shabbat between Rosh HaShanah and Yom Kippur is called Shabbat Shuva. Sefer HaTodaah (The Book of Our Heritage) explains there are two reasons for this name. On a simple level, the opening words of the Haftarah for this Shabbat are “Shuva Yisrael Ad hashem Elokecha,” “Return, Israel to hashem your G-d.” This choice of words teaches us that everyone has to repent. As Shlomo HaMelech assures us (Kohelet 7:20), there is no one so righteous that he has never sinned and is not in need of repentance, and there is no one so thoroughly corrupt that he cannot repent (as Rabbeinu Yonah informs us many times in his Shaarei Teshuva).
Another reason why this Shabbat is called Shabbat Shuva is because it occurs during the Aseret Yemei Teshuva, the Ten Days of Repentance. For this reason, it is customary for the Rabbi of every shul to give a Shabbat Shuva Drasha wherein the Rav expands upon the concepts of Teshuva and emphasizes the gravity of sinning so that the people will turn their hearts toward doing Teshuva. In general, Shabbat is a time for learning Torah and davening, and a person should be even more attentive to learning Torah, davening, and reflecting upon Teshuva this Shabbat, to atone in some way for improper actions on previous Shabbatot that year (see the Drashot Yaarot Devash, cited in the Mishnah Berurah 603:2).
Shabbat Shuva is a wake up call for us to repent. Will we heed it?