Yaakov's emes illuminates the night

ויפגע במקום שתיקן תפלת ערבית.

"And he encountered the place" — this refers to Yaakov instituting the evening tefillah (Maariv).

Chazal learn from this posuk that Yaakov was the one who established the davening of nighttime, the avodah of serving Hashem even when His light is hidden.

דכתיב שפת אמת תכון לעד.

As it is written: "The lip of truth shall be established forever" (Mishlei 12:19).

The midah of emes (truth) is something that lasts permanently and is never uprooted.

ולכן מדתו של יעקב דכ' ביה תתן אמת ליעקב הוא נוקב ויורד עד התהום כמ"ש תפלת ערב אין לה קבע וזמנה כל הלילה.

Therefore the midah of Yaakov, of whom it is written "You shall give truth to Yaakov" (Michah 7:20), bores down and descends to the very depths — as Chazal said, the evening tefillah has no fixed time and its zman is the entire night.

Because emes reaches all the way to the lowest places, Yaakov's avodah can penetrate even the darkness of night, where there is no set boundary.

כי תפלת שחרית ומנחה היא בזמן מיוחד אבל תפלת ערבית היא לעולם.

For Shacharis and Minchah have a designated time, but Maariv is forever.

The daytime davenings are bounded by particular hours, but the avodah of the night has no limit — it represents serving Hashem in every situation.

ואיתא בזוה"ק כוננת לעד לא כתיב רק תכון זמינא דיתקן כו' ע"ש.

And it is brought in the Zohar Hakadosh: it does not say "You established it forever," only "it shall be established" — meaning it is destined to be set right, etc. See there.

The Zohar reads "tikon" (shall be established) in the future tense, teaching that the rectification is something that will yet be revealed.

פי' שכל עובד ה' באמת יש לו להאמין כי נשאר לו מזה תיקון הגם שאינו מתגלה בפועל ממש.

The explanation is that every person who serves Hashem in truth must have emunah that a tikkun (rectification) remains from his avodah, even though it is not actually revealed in practice.

Even when one cannot see results from his avodah, he should believe with emunah that nothing of genuine service to Hashem is ever lost — a lasting impression remains.

ואיתא כי יעקב נכנס בעובי הקורה וע"י שהי' איש אמת לגמרי הי' יכול להכניס עצמו בכל המקומות לברר האמת מן השקר וכל החושך ברח מפניו והוא בחי' שבת כמ"ש חז"ל יעקב שכתוב בו שמירת שבת.

And it is brought that Yaakov entered into the thick of the beam, and because he was completely a man of truth he was able to bring himself into all places to separate the truth from the falsehood, and all the darkness fled before him — and this is the aspect of Shabbos, as Chazal said that Yaakov is the one of whom shemiras Shabbos is written.

Because Yaakov was wholly emes, he could descend into any place, even the lowest, to sort out the truth from the falsehood there, and the concealment automatically dissolved before him — this is the quality of Shabbos, the day of clarity and truth.

וזהו עצמו הרמז ויצא יעקב מבאר שבע שהוא השבת אור שבעת הימים ובזה הכח תיקן כל ימי המעשה שהשבת נותן הארה לתקן כל הימים כי בכל יום יש ערב ובוקר.

And this itself is the hint in "And Yaakov went out from Be'er Sheva" — which alludes to the Shabbos, the light of the seven days, and with this power he rectified all the weekdays, for the Shabbos gives illumination to repair all the days, since every day has an evening and a morning.

"Be'er Sheva" hints at the "well of seven," the Shabbos which is the source of light for the whole week; from Shabbos one draws the power to elevate and fix each weekday, every one of which contains both darkness (evening) and light (morning).

ושבת כולו אור כי טוב.

But Shabbos is entirely light — "for it is good."

Unlike the weekdays which mix evening and morning, Shabbos is wholly luminous, pure good with no darkness.

ראי' לדבר דיש בכל איש ישראל ב' אותות מילה ותפילין ובשבת מילה ושבת.

A proof to the matter: every Jew has two signs — milah (circumcision) and tefillin — and on Shabbos, milah and Shabbos itself.

The "os" (sign) of the covenant takes different forms; during the week it is tefillin, but on Shabbos the day itself serves as the second sign in place of tefillin.

ומצות תפילין מימים ימימה למעט לילות שאין אור התפילין מתגלה בלילה.

And the mitzvah of tefillin is "from days to days" — to exclude nights, for the light of tefillin is not revealed at night.

Tefillin are worn only in the daytime, because their illumination cannot be revealed during the darkness of night.

אבל אות שבת שהוא כמו תפילין מאיר ביום ובלילה וכן מזה הכח יכולין לקבל הארה לתקן כל הלילות:

But the sign of Shabbos, which is like tefillin, shines both by day and by night; and likewise from this power one is able to receive illumination to rectify all the nights.

Because the holiness of Shabbos shines even in the dark, it gives a person the strength to bring Hashem's light into the "nights" — the concealed, difficult times — and rectify them too.

Summary: Yaakov's midah of emes, expressed in the nighttime davening of Maariv, has the power to penetrate even the darkness and the lowest places; this is the aspect of Shabbos, the light of the seven days, from which Bnei Yisrael draw the strength to rectify all the weekdays and even all the "nights" of concealment.