Reclaiming Holy Sparks at Sinai
וישב ממנו שבי דרשו חז"ל שפחה אחת
"And he took some of them captive" (Bamidbar 21:1) — Chazal expounded that this refers to a single maidservant.
The pasuk says the Canaanite king of Arad took captive from Bnei Yisrael, and Chazal narrow this to only a single maidservant, hinting that what the nations can seize from Bnei Yisrael is exceedingly small and pointing toward a deeper meaning.
דכ' עלית למרום שבית שבי
This is connected to the pasuk "You ascended on high, You took captivity captive" (Tehillim 68:19).
The Sfas Emes links this "captivity" to the pasuk about ascending on high to receive the Torah and "taking captivity captive," suggesting the two captivities are spiritually related.
פי' דבקבלת התורה הוציאו בנ"י כל הנ"ק שהיו בתוך האומות וז"ש ה' מסיני בא וזרח משעיר למו כו' אותו החלק והצד אחיזה שיש לע' אומות בתורה
The meaning is that through the receiving of the Torah, Bnei Yisrael drew out all the holy sparks (nekudos kedushah) that were embedded within the nations; and this is the meaning of the pasuk "Hashem came from Sinai and shone forth to them from Seir" (Devarim 33:2) — referring to that portion and that foothold of grasp which the seventy nations have within the Torah.
When Bnei Yisrael received the Torah, they reclaimed the holy sparks scattered among the nations; the Torah's light shining "from Seir" alludes to the limited share of grasp the seventy nations once held in it.
כי הלא נק' ראשית וע"כ יש איזה נקודה שמתפשט להם מהתורה והכל נמסר לבנ"י וע"ז כתיב וישב ממנו שבי אותו השבי שלקחו בנ"י מהם
For behold, [the Torah] is called "reishis" (the first), and therefore there is a certain point that extends to them from the Torah; yet ultimately all of it is handed over to Bnei Yisrael, and concerning this it is written, "and he took some of them captive" — that captivity being precisely what Bnei Yisrael took back from them.
Because the Torah is called "reishis," some faint point of it does extend even to the nations, but in the end the whole of it reverts to Bnei Yisrael — and this reclaiming is the true inner meaning of the "captivity" that Bnei Yisrael took from them.
ומזה הבינו בנ"י כי השבעה אומות אין בהם נקודה של אמת
And from this Bnei Yisrael understood that within the seven nations there is no point of truth (nekudah shel emes) at all.
From this very episode Bnei Yisrael grasped that the seven Canaanite nations contain no genuine point of truth that could endure.
לכן נדרו אם נתן תתן כו' והחרמתי כו' כמו שנצטוו אח"כ לא תחי' כל נשמה
Therefore they vowed, "If You will indeed deliver this people into my hand... then I will utterly destroy [their cities]" (Bamidbar 21:2), just as they were later commanded, "You shall not allow any neshamah to live" (Devarim 20:16).
This recognition is why Bnei Yisrael vowed the cherem of utter destruction, anticipating the later command of the Torah to leave no neshamah of these nations alive, for there was nothing of lasting truth left to preserve.
וכוונו בנ"י מעצמן לזאת המצוה מאחר שלא הי' קיום לאותו השבי ששבו מהם כנ"ל
And Bnei Yisrael directed themselves to this mitzvah of their own accord, since there was no enduring existence for that captivity which they had taken back from them, as explained above.
Bnei Yisrael came to this mitzvah on their own initiative, understanding that whatever the nations had captured from them had no lasting hold, and so the nations themselves had no enduring spiritual basis.
אח"כ מצאתי קצת מזה בזוה"ק דף קצ"ג ע"ש:
Afterward I found a portion of this matter in the holy Zohar, folio 193 — see there.
The Sfas Emes closes by noting that he later found support for this idea in the holy Zohar, folio 193, and directs the reader to consult that source.
Summary: This piece reinterprets the Canaanite king's brief capture of Bnei Yisrael in the midbar as a spiritual mirror of the Torah's own "taking captivity captive" at Sinai. The Sfas Emes explains that since the Torah is called "reishis," the seventy nations held only a faint, borrowed point of its light, and when Bnei Yisrael received the Torah they reclaimed all the holy sparks that had been dispersed among the nations. Once those sparks were withdrawn, the seven Canaanite nations were left empty of any point of truth, which is why Bnei Yisrael vowed to destroy them utterly, anticipating the later command of the Torah to spare no neshamah among them. Bnei Yisrael reached this commitment of their own accord, grasping that nothing of enduring value remained in nations stripped of their inner truth. The Sfas Emes notes that he afterward found corroboration for this teaching in the holy Zohar.