Sforno on Deuteronomy 30:9/ספורנו על דברים ל׳:ט׳

1'והותירך ה, He will grant you success beyond any success you have ever enjoyed previously.

2לטובה...הכתובה בספר התורה הזה, as He said when He said: והתהלכתי בתוככם והייתי לכם לאלוקים ואתם תהיו לי לעם, “I shall walk freely in your midst and will be your G’d and you will be My people” (Leviticus 26,12) This promise will be fulfilled when כאשר ה' ישוב לשוש עליך...לטוב כי תשמע, as He had once delighted in your forefathers (the patriarchs). This time the good you will experience at G’d’s hands will not be due to the merit of the patriarchs but will be due to the fact that your repentance is so wholehearted and unreserved. Due to your unreserved repentance your former demerits will be converted into merits, seeing that it was, after all, these demerits and what followed that have become the catalyst of your eventual return to G’d. You will enjoy G’d’s goodwill just as did the patriarchs.