Selfless servanthood earns the Shabbos neshamah

במדרש עבד משכיל כו'.

In the Midrash: "A wise servant (eved maskil)" etc. (Mishlei 17:2).

The Sefas Emes opens from the pasuk praising the servant who serves with understanding.

פי' משכיל בעבודתו שאינו ע"מ לקבל פרס רק נותן נפשו להצליח בשליחותו וזו המעלה יתירה שיש לבנ"י גם בבחי' עבדות כמ"ש עבדי הם כי בבחי' בנים אין שייכות לשום אומה.

The explanation: he is "wise" in his avodah, for he does not serve in order to receive reward (pras), but rather gives over his very soul to succeed in his shlichus (mission) — and this is the additional virtue that Bnei Yisrael possess even in the aspect of servanthood, as it says, "for they are My servants" (Vayikra 25:55); for in the aspect of being "children" there is no comparison to any nation.

The greatness of Bnei Yisrael as Hashem's servants is that they serve selflessly, not for reward — a distinction visible specifically in their role as avadim, since their status as Hashem's children is beyond any comparison at all.

וזה רמז בן מביש שבקבלת התורה שנקראו בני ישראל בנים ביישו את כל העולם.

And this is hinted in "a son who causes shame" (ben mevish) — that at Kabbalas HaTorah, when Bnei Yisrael were called "children," they put the whole world to shame.

When Israel became Hashem's "children" at Sinai, their elevation shamed all the nations who had refused the Torah.

אבל בגלות בבחי' עבדות עדות יתירה על בנ"י שהם עבד משכיל.

But in galus, in the aspect of servanthood, there is an additional testimony about Bnei Yisrael — that they are a "wise servant."

In exile, when only the servant-relationship is visible, Israel's selfless devotion bears even greater witness to their loyalty.

ומעין זה בימי המעשה עם השבת כי שבת בחי' בנים שמתגלה כח הנשמה ירא שבת ירא בשת שהארת הנשמה מבייש לכל אוה"ע כי אין נשמה רק לבנ"י.

And something of this same pattern exists between the weekdays and Shabbos: for Shabbos is the aspect of "children," when the power of the neshamah is revealed — "one who fears Shabbos (yarei Shabbos)" is "one who fears shame (yarei bosheth)," for the illumination of the neshamah shames all the nations, since there is a neshamah only to Bnei Yisrael.

Shabbos corresponds to the "children" relationship, when the neshamah shines forth — a light unique to Israel that puts the nations to shame, just as the Sinai revelation did.

ובימי המעשה בחי' עבד.

And on the weekdays there is the aspect of "servant."

The working days correspond to the lower, servant-relationship with Hashem.

אבל כשהעבדות בהשכל שלא על מנת לקבל פרס ימשול בבן מביש.

But when the servanthood is carried out with understanding (haskel), not in order to receive reward, then "he will rule over the son who causes shame" (Mishlei 17:2).

When a person serves through the weekdays selflessly, his "servant" avodah gains mastery over and merits the higher "son" level of Shabbos.

ולכן כפי עבודת ימי המעשה כך זוכין להנשמה בשבת:

Therefore, according to one's avodah during the weekdays, so does one merit the neshamah on Shabbos.

The selfless toil of the week is precisely what earns the revelation of the Shabbos neshamah.

Summary: Bnei Yisrael have two relationships with Hashem — "children" and "servants." The servant level shines specifically in galus and on weekdays, where serving selflessly without seeking reward is the true greatness of the eved maskil. This devoted weekday avodah is what merits the higher "children" level — the revelation of the neshamah on Shabbos, whose light, like the giving of the Torah, distinguishes Israel from all the nations.