But we do not read the קללות שבמשנה תורה (the תוכחה in כי תשא) right before ראש השנה; we read it last week. תוספות asks this, but to understand his question we need to learn some background.
The cycle of Torah reading is set up so that we finish reading with וזאת הברכה on Simchat Torah. The Shabbat before that is on Sukkot, so we read a portion related to the Yom Tov. Yom Kippur comes 4 days before Sukkot, so some years there is a Shabbat in there and some years not. Before that is Shabbat Shuva, and before that is the Shabbat preceding Rosh Hashana. In a year without a Shabbat betwen Yom Kippur and Sukkot (like this year), Haazinu is read on Shabbat Shuva and Nitzavim-Vayelech is read before Rosh Hashana. In a year with a Shabbat between Yom Kippur and Sukkot, Haazinu is read on that Shabbat and we split Nitzavim and Vayelech so that Vayelech is read on Shabbat Shuva and Nitzavim in read the week before Rosh Hashana. So we always read Nitzavim before Rosh Hashana, even though it means creating these incredibly tiny parshiot (30-52 psukim) to make them fit. Why not split some of the really long ones earlier in Devarim, especially when the Gemara implies that we should?
But how can we say לא תהא מדברת בקללות כלל? נצבים has some very dramatic curses:
Rabbi Shlomo Spiro of the Elizabeth Kollel gives an answer:
So the curses of our parasha are not listed for their own sake, but to introduce the idea of תשובה, that even after all these terrible things, there is a chance for redemtion:
It certainly seems to talk about “returning” a lot. There’s a rhetorical device called polyptoton for this kind of thing; repeating the same root in different forms to add emphasis. But in Tanach this kind of repetition is deeper; it reflects the central meaning of the text. Martin Buber coined the word leitwort, leading word, מִילָה מַנְחָה, for this when he wrote his German translation of תנ״ך. Umberto Cassuto (who was a professor at Hebrew University in the 1930’s) noted that they tended to come in sevens or multiples of sevens. In our psukim, the root שוב occurs exactly seven times.
So what does this mean? Specifically, how would we translate והשבת אל לבבך and שבת עד ה׳ אלקיך? Is is “you will return to ה׳” or “you shall return”? As any grade school grammar teacher will tell you, “you will” is a statement about the future, an assurance that it will happen. “You shall” is command (“Thou shalt not kill”). (As an aside, it’s one of those rules that only grade school grammar teacher hold; it’s never been actually true for real English). Is this paragraph describing a מצוה of תשובה or is it reassuring us that no matter what, we will be able to return to ה׳?
The JPS translation (probably the most careful about the English) treats this as a commandment:
The Rambam says these psukim are a promise, not a commandment:
He doesn’t seem to hold that there is a specific mitzvah to do teshuva; it’s just the mechanism for undoing the damage done by sin. The mitzvah of teshuva is in the mechanics:
The question of whether the Rambam holds there is a separate mitzvah of teshuva is complex; see the articles by Rabbi Ross and Rabbi Tabory.
The Ramban looks at the context of these psukim:
What does the היא of לא בשמים הוא refer to? We usually interpret it with רש״י as “the whole Torah”, as in the famous story of the תנור של עכנאי:
But the Ramban points out that the Torah refers to המצוה הזאת:
The Ramban has a nuanced approach to our psukim. There is a commandment, but it is worded with this will/shall ambiguity because ה׳ is also making a promise. No matter how dire the straits, we will be able to do teshuva and ה׳ will accept it.
The psukim themselves seem to be out of order. They go back and forth between “you” (בני ישראל) returning to ה׳ and ה׳ returning them to their land; it starts with the promise of תשובה (ושבת עד ה׳ אלקיך) and after, all the response from ה׳, talks about תשובה again (תשוב אל ה׳ אלקיך).
Complete תשובה, erasing our entire past, is impossible. It can only happen in stages, with the active help of הקב״ה.
The first level of תשובה is simply והשבת אל לבבך, thinking about it (what experts in addiction call the ”contemplative“ stage). This is ושבת עד ה׳, not אל ה׳, not all the way, but just heading toward ה׳.
The next stage is “preparation”, doing what is necessary to make the change. Here that is תשוב ושמעת בקול ה׳ ועשית את כל מצותיו; doing the mitzvot, even without a true change of heart. Hypocrisy in this sense is not a sin, but a necessary first step. As the ספר החינוך says (מצוה טז) אחרי הפעולות נמשכים הלבבות.
And ה׳ will remove the impediments that keep us from complete תשובה, אם אתה פותח כחודה של מחט, הנה הוא יפתח לך כפתחו של אולם, and we can reach the “action” stage of תשוב אל ה׳ בכל לבבך ובכל נפשך.