The extra soul of Shabbos awakens teshuvah

וכתבו חז"ל שבת ניתן בצינעא דכתיב ביני ובין בני ישראל כו' א"ה לא ליענשו א"ה כו' נשמה יתירה לא אודיעינהו כו' וינפש וי אבדה נפש כו'.

And Chazal wrote that Shabbos was given in private (be-tzin'ah), as it is written "between Me and Bnei Yisrael" (Shemos 31:17); [the Gemara asks] if so, [the nations] should not be punished [for not keeping it] — if so, etc.; "the extra soul (neshamah yeseirah) I did not make known to them," etc.; "and He rested (va-yinafash)" — "woe, the soul is lost (vai avdah nefesh)," etc. (Beitzah 16a).

The Gemara teaches that Shabbos was given to Bnei Yisrael privately — a hidden gift, including the secret of the neshamah yeseirah (the extra soul of Shabbos) not disclosed to the nations. It darshens "va-yinafash" as "vai avdah nefesh" — woe over the soul that is lost at Shabbos's departure.

ומקשין כי ענין וינפש שייך במוצאי שבת.

And they raise a difficulty: that the matter of "va-yinafash" [the loss of the extra soul] is relevant [only] at the conclusion of Shabbos (motza'ei Shabbos).

The problem: the "woe, the soul is lost" applies to the departure of the neshamah yeseirah at Shabbos's end — yet the verse "va-yinafash" speaks of Shabbos itself, not its conclusion.

אך משמעות הגמ' הנ"ל כי אין נודע בחי' נשמה יתירה רק בשבת.

But the implication of the aforementioned Gemara is that the aspect of the neshamah yeseirah becomes known only on Shabbos [itself].

The resolution: one can only become aware of the extra soul while it is present on Shabbos; the awareness of it belongs to Shabbos itself, even though its loss is felt afterward.

ולכך כיון שלא ניתן השבת לאוה"ע.

And therefore, since Shabbos was not given to the nations of the world.

Because the nations were never granted Shabbos.

אין יכולין לידע בחי' נשמה יתירה.

They cannot know the aspect of the neshamah yeseirah.

Lacking Shabbos, the nations have no access to the experience of the extra soul at all.

ולכך כתיב בשבת וינפש.

And therefore "va-yinafash" is written regarding Shabbos [itself].

The verse fittingly places "va-yinafash" on Shabbos, because the very awareness of the soul — and thus of its eventual loss — only arises during Shabbos.

כי בשבת כשנרגיש בחי' נשמה יתירה.

For on Shabbos, when we sense the aspect of the neshamah yeseirah.

It is on Shabbos that a person actually feels the presence of the additional soul.

אז ע"י שיודעין שבחול נחסר זה.

Then, through knowing that during the weekdays this is lacking.

Sensing the extra soul on Shabbos makes one keenly aware of how much is missing during the ordinary week.

יכולין לבוא לבחי' תשובה.

One is able to come to the aspect of teshuvah.

That awareness of the weekday's deficiency awakens a person to teshuvah — a longing to repair and reconnect.

ועי"ז יהי' נמשך הארה גם לימות החול.

And through this, illumination will be drawn down also to the weekdays.

The teshuvah awakened on Shabbos draws Shabbos's light forward into the coming weekdays, elevating them too.

ובשם הבעש"ט כתבו כי נכתב זה בשבת שע"י שיודעין זה בשבת.

And in the name of the Baal Shem Tov they wrote that this was written regarding Shabbos, because through knowing this on Shabbos.

The Sefas Emes cites the Baal Shem Tov on why "va-yinafash" is stated about Shabbos itself: because the awareness is gained on Shabbos.

כי בחול ניטל זה.

That during the weekday this [extra soul] is taken away.

One realizes on Shabbos that this precious soul will be removed during the workweek.

משמרין יותר יום שבת שלא לילך בטל בעת מצוא הנשמה יתירה המסייעת לעבודתו ית' ע"כ:

One guards the day of Shabbos more carefully, so as not to go about idle at the time when the neshamah yeseirah is found, which assists in His avodah.

Knowing the extra soul is present and aids one's avodah, a person is moved to cherish and guard Shabbos all the more — not to squander it in idleness while this soul, which empowers his service of Hashem, is available.

Summary: Shabbos was given to Bnei Yisrael privately, including the hidden gift of the neshamah yeseirah, unknown to the nations. The Gemara's "va-yinafash" ("woe, the soul is lost") is written about Shabbos itself — not only its departure — because the extra soul can be perceived only while present on Shabbos. Sensing it makes one aware of the weekday's deficiency, awakening teshuvah and drawing Shabbos's light into the week. In the Baal Shem Tov's name: this very awareness should move a person to guard Shabbos and not waste the precious time when the extra soul is present to aid his avodah.