Ve’shavta ad Hashem Elockecha ve’shomata be’Kolo ke’chol asher Anochi metzavecha hayom….”—You shall return to Hashem your G-d and listen to His voice, …Then Hashem your G-d will bring back your captivity and have mercy upon you, and He will gather you from all the peoples to which Hashem your G-d has scattered you” (Devarim 30: 2-3).
Sefer Noam Megadim explains: The first step of teshuva, after abandoning sin, is accepting the yoke of Shabbos and being scurplous in its observance, because one who desecrates Shabbos is equivlant to an idol worshipper.
Chazal say that if Bnei Yisrael would observe two succsesive Shabbosos, they would be redeemed immediately. The Zohar explains that this really relates to one Shabbos, because every Shabbos has two parts─ Shabbos night, and Shabbos day.
Accordingly we can explain the phrase: “Ve’shavta ad Hashem Elokecha”: The first step you shall take after doing teshuva is “ve’shomata be’kolo kechol asher ani me’tzavcha hayom,” implying that you should hearken to Hashem’s voice for one full Shabbos. In that manner Hashem will immediately return to you. As a result of “shvisa” – ceasing of work — He will return to you.