Root Generation Teshuvah Power
בפסוק ועתה כתבו לכם כו' וענתה השירה הזאת לפניו כו'
On the verse, "And now, write for yourselves [this song]... and this song shall testify before it..." (Devarim 31:19-21).
The Sfas Emes opens with the verse commanding Bnei Yisrael to write the song of Haazinu, which will serve as a testimony before them.
כי קודם החטא הי' השכינה שרוי' בתוך בנ"י בהתגלות
For before the sin, the Shechinah dwelled within Bnei Yisrael in a revealed manner.
Before the first sin, Hashem's Presence was openly felt dwelling among Bnei Yisrael.
ובעת הגלות כ' ואמר כו' אין אלקי בקרבי כו' הסתר אסתיר כו'
But at the time of the exile it is written, "And he will say... 'Is it not because my God is not in my midst...'" (Devarim 31:17), and "I will surely hide [My face]" (Devarim 31:18).
Once galus set in, the Torah describes Hashem concealing His Presence, so that a person feels as if Hashem is no longer in his midst.
אבל הש"י נמצא לבנ"י באמצעיות התורה
Yet Hashem is found by Bnei Yisrael through the medium of the Torah.
Even in this hiddenness, Bnei Yisrael can still reach Hashem — through the Torah, which becomes the channel to His Presence.
והקב"ה צוה למרע"ה לגנוז כל ההארות בתוך הספר תורה
And the Holy One, Blessed is He, commanded Moshe Rabbeinu to conceal all the lights within the Sefer Torah.
Hashem instructed Moshe Rabbeinu to embed and hide all the spiritual lights within the Sefer Torah itself.
ולכן נק' התורה עדות שהשכינה שורה בישראל
Therefore the Torah is called "testimony," for it testifies that the Shechinah rests upon Bnei Yisrael.
Because those lights are stored within it, the Torah is termed a "testimony" — living proof that the Shechinah rests upon Bnei Yisrael.
וע"י היגיעה בתורה מתגלה הארת הקדושה וכ' וענתה מלשון עני' ע"י אתערותא דלתתא
And through toiling in Torah the light of kedushah is revealed, and it is written, "and it shall answer" (ve'ansah), from the language of "responding" (aniyah) — through an arousal from below.
When a person toils in Torah, that hidden kedushah is drawn out; the word "ve'ansah" hints that the light "answers" the person's effort, an awakening from below that draws a response from Above.
ועתה הוא לשון תשובה
And "And now" (ve'atah) is a term denoting teshuvah.
The Sfas Emes notes that the word "ve'atah" ("and now") carries the meaning of teshuvah, a fresh return to Hashem in the present.
ויתכן לרמוז כי הקב"ה אמר למרע"ה שהדור שלהם הי' השורש שהכל תלוי בהם
And it is fitting to hint that the Holy One, Blessed is He, told Moshe Rabbeinu that their generation was the root upon which everything depends.
He suggests a deeper hint: Hashem told Moshe Rabbeinu that the generation of the midbar was the spiritual root from which all later generations draw, so everything hinges upon them.
והוצרכו המה לשוב גם על החטאים של דורות האחרונים והי' התשובה עוד קודם החטא
And they needed to do teshuvah even for the sins of the later generations, and this teshuvah came even before the sin.
Because they were the root, they had to do teshuvah even on behalf of the sins of future generations, and remarkably this teshuvah preceded the sins themselves.
והענין היא שע"י החטאים שהי' בדור הראשון הגם שהי' חטאים קלים לפי רוב עונות דורות האחרונים
And the matter is that through the sins committed in the first generation — even though these were light sins compared to the abundant transgressions of the later generations —
The point is that the relatively minor sins of that first, lofty generation — slight compared to the heavier sins of later eras —
עכ"ז הכל תלוי בהשורש
nevertheless, everything depends upon the root.
still carry decisive weight, because whatever happens at the root affects everything that grows from it.
ולכן הראה להם הקב"ה מה שיהי' לסוף באחרית הימים ועשו תשובה ובכח התשובה שלהם יכולין אנו להתעורר לתשובה ולכן כתב זה אצל פרשת התשובה כנ"ל
Therefore the Holy One, Blessed is He, showed them what would be at the end of days, and they did teshuvah, and through the power of their teshuvah we are able to be aroused to teshuvah; and therefore this was written alongside the parshah of teshuvah, as above.
Hashem therefore showed that first generation the future end of days so they could do teshuvah in advance; the strength of their teshuvah empowers us to be aroused to teshuvah, which is why this is placed beside the parshah of teshuvah.
לכן מקודם כ' אתם נצבים כו' ומסיים לא אתכם לבדכם כו'
Therefore beforehand it is written, "You are standing [today, all of you]..." (Devarim 29:9), and it concludes, "Not with you alone [do I forge this covenant]..." (Devarim 29:13).
This explains why the Torah first says "You are standing today, all of you," emphasizing the unity of the generation, and then adds "Not with you alone do I forge this covenant."
הוא כנ"ל שעל ידיהם כורת ברית עם כל הדורות:
This is as above, that through them He forges a covenant with all the generations.
As explained, through this root generation Hashem forged the covenant with every later generation as well.
Summary: The Sfas Emes explains that before the first sin, the Shechinah dwelled openly among Bnei Yisrael, but in galus Hashem conceals His Presence so that He seems absent. The remedy is the Torah, into which Moshe Rabbeinu was commanded to conceal all the spiritual lights, which is why it is called a "testimony" that the Shechinah rests upon Bnei Yisrael; through toil in Torah those lights "answer" our arousal from below. He then reads "ve'atah" as a hint to teshuvah, explaining that the generation of the midbar was the spiritual root of all later generations, so they did teshuvah in advance even for sins not yet committed. Because everything depends on the root, Hashem showed them the end of days and they returned, and the power of their teshuvah empowers every later generation to do teshuvah. This is why the parshah first stresses "You are standing today, all of you" and then "Not with you alone do I forge this covenant" — through this root generation Hashem binds Himself in covenant with all the generations.