Rise and fall between nefesh and ruach

בפסוק אספה לי שבעים איש ובמד' שהיו אותן השוטרים שבמצרים דכתיב בשבעים נפש ירדו כו' מצרימה וזהו המספר בשבעים הוא בחי' נפש ובזה הי' בגלות מצרים.

On the verse "Gather for Me seventy men" — and in the Midrash, that these were those same officers who had been in Mitzrayim, as it is written, "With seventy souls (nefesh) your forefathers went down… to Mitzrayim"; and this number, seventy, is the aspect of nefesh, and on this level they were during the galus of Mitzrayim.

The seventy elders gathered to assist Moshe are linked to the seventy souls who originally descended to Mitzrayim. The Sefas Emes reads "seventy" as representing the level of nefesh, the lowest soul-rung, which was the spiritual state of Bnei Yisrael during the Egyptian galus.

אח"כ נתעלו לבחי' רוח זהו בחי' י"ב שבטים ד' דגלים לד' רוחות.

Afterward they were elevated to the aspect of ruach — this is the aspect of the twelve tribes, four banners for the four directions (ruchos).

After the redemption they rose from nefesh to the higher level of ruach. This is reflected in the organization of the twelve shevatim into four degalim (banners) arrayed to the four "ruchos" (winds/directions), a play on ruach.

ובבחי' זו כתיב בהתאסף ראשי כו' יחד שבטי ישראל.

And concerning this level it is written, "When the heads of the people gathered, the tribes of Yisrael together" (Devarim 33:5).

This elevated, unified state of the tribes is described by the verse depicting all the shevatim joined together as one under their leaders.

ואחר החטא נפלו ממדריגה זו ואמרו נפשנו יבשה שלא היו יכולין להמשך אחר מדריגת משה רבינו ע"ה שהוריד להם המן מאכל מלאכי השרת דכתיב בהם עושה מלאכיו רוחות כו'.

But after the sin they fell from this level and said, "Our soul (nafsheinu) is dried up," for they could no longer be drawn after the level of Moshe Rabbeinu, peace be upon him, who brought down for them the mann, the food of the ministering angels, of whom it is written, "He makes His angels winds (ruchos)."

After the sin of complaining, Bnei Yisrael fell back down, declaring "our nefesh is dried up." They could no longer keep pace with Moshe's lofty madreigah of ruach — the level reflected in the mann, "bread of angels," whom Hashem makes into "ruchos."

וירדו לבחי' נפש והוצרך להיות הנהגתם בבחי' שבעים איש הנ"ל.

And they descended to the aspect of nefesh, and therefore their leadership had to be in the aspect of the aforementioned seventy men.

Having dropped back to the level of nefesh, they now required a mode of leadership matching that level — hence the appointment of the seventy elders, who correspond to that lower "nefesh" rung.

ויש רמז בפסוק בלתי אל המן עינינו כו' ושם כתיב זובח לאלהים יחרם בלתי לה' לבדו כי בחי' הנהגת מרע"ה הוא בשם הוי"ה.

And there is a hint in the verse "there is nothing at all (bilti), only the mann before our eyes" — and elsewhere it is written, "One who sacrifices to gods shall be destroyed, only (bilti) to Hashem alone" — for the mode of leadership of Moshe Rabbeinu is through the Name Havayah (the Tetragrammaton).

The Sefas Emes links the word "bilti" (only/nothing but) in the people's complaint to its appearance in the verse demanding exclusive devotion to Hashem alone. Moshe's leadership operated through the Name Havayah, which expresses pure, undivided unity with Hashem.

והם לא היו יכולין להימשך אחר זה האחדות השלימה ודו"ק:

And they were not able to be drawn after this complete unity. Examine this well.

Having fallen to the level of nefesh, the people could no longer attach themselves to the perfect unity (achdus) embodied in Moshe's leadership through the Name Havayah, and so needed the more accommodating leadership of the seventy.

Summary: The seventy elders correspond to the seventy souls who descended to Mitzrayim and to the level of nefesh — the spiritual rung of Bnei Yisrael in galus. After the redemption they rose to ruach, reflected in the unified twelve tribes and four banners; but after their sin they fell back to nefesh, unable to keep pace with Moshe Rabbeinu's leadership of perfect unity through the Name Havayah, and so required leadership on the level of the seventy.