Awakening the Time of Favor
ואני תפלתי לך ה' עת רצון קבעוהו במנחת שבת שהיא עת רצון
"As for me, may my tefillah to You, Hashem, be at an eis ratzon (time of favor)" (Tehillim 69:14) — the Chachamim fixed this verse in the Minchah of Shabbos, for it is an eis ratzon.
The Chachamim placed this verse, which asks that tefillah arrive at an eis ratzon, into the Shabbos Minchah precisely because that moment is itself a time of Divine favor.
והאמת כי בנ"י מעוררין בתפלתם עת רצון כמו שדרשו חז"ל אימתי עת רצון כשציבור מתפללין
And the truth is that Bnei Yisrael arouse the eis ratzon through their tefillah, as Chazal expounded: When is the eis ratzon? When the tzibbur (congregation) is davening.
Chazal teach that the eis ratzon is not merely a fixed moment we happen upon; it is Bnei Yisrael who generate it through their communal tefillah, for the favor comes about when the tzibbur davens.
וז"ש ואני תפלתי לך כו' עת רצון שהתפלה גורמת הרצון
And this is the meaning of "As for me, may my tefillah to You be at an eis ratzon" — that the tefillah itself brings about the ratzon (favor).
The verse is read to mean that our tefillah does not merely coincide with the ratzon but actually causes it.
רק מ"מ יש עתים שהקב"ה משתוקק לרצון זה שבנ"י יגרמו רצון
Yet nevertheless there are times when the Ribono shel Olam Himself yearns for this very ratzon, that Bnei Yisrael should be the ones to bring about the favor.
Even so, there is a deeper level in which the Ribono shel Olam Himself longs that Bnei Yisrael should be the ones to call forth His favor, making their avodah something He desires.
וזה רעוא דרעוין שהקב"ה יש לו רצון שיעוררו בנ"י עת רצון כנ"ל
And this is the meaning of "the favor of all favors" (ra'ava d'ra'avin) — that the Ribono shel Olam has a ratzon that Bnei Yisrael should arouse the eis ratzon, as explained above.
This Divine longing is what the Zohar calls the "favor of all favors" — Hashem's own ratzon that Bnei Yisrael arouse the eis ratzon, the highest expression of Divine favor.
ובשבת קודש שיש להקב"ה נייחא מהבריאה ע"י בנ"י שמעידין שברא עולמו בששה ונח בשביעי וזהו הרצון נותן חיות לכל השבוע הבאה
And on Shabbos Kodesh, when the Ribono shel Olam has, as it were, naycha (repose) from the work of Creation through Bnei Yisrael — who testify that He created His world in six days and rested on the seventh — this is the ratzon that gives chiyus (life-force) to the entire week that follows.
On Shabbos, Bnei Yisrael grant Hashem a kind of repose by testifying through their rest that He created the world in six days and rested on the seventh, and this Shabbos ratzon then channels chiyus into the whole coming week.
ולכן צריך האדם להשתוקק להשי"ת בסוף יום השבת לבקש שלא יהי' נפרד ע"י מעשים של חול וכמו מסירת מודעא קודם המעשה:
And therefore a person must yearn for Hashem Yisbarach at the close of the Shabbos day, to entreat that he not become separated from Him through the deeds of the weekday — like the lodging of a mesiras moda'a (a prior declaration) before the act.
Since the weekday deeds threaten to pull a person away from this dveikus, at Shabbos's end he should yearn for Hashem and entreat not to be severed by mundane activity — declaring his true intent in advance, like a mesiras moda'a registered before an act.
Summary: In this piece the Sfas Emes explains why the verse "va'ani sefillasi" was fixed in the Shabbos Minchah, the great eis ratzon: it is Bnei Yisrael themselves who, through their communal tefillah, arouse and bring about Hashem's favor, as Chazal teach that the eis ratzon comes when the tzibbur davens. Beyond this, he reveals a deeper layer — that the Ribono shel Olam Himself yearns for Bnei Yisrael to be the ones to call forth this ratzon, and this is the meaning of ra'ava d'ra'avin, the favor of all favors. On Shabbos this reaches its height, for Bnei Yisrael give Hashem repose by testifying to the six days of Creation and the rest of the seventh, and that ratzon then pours chiyus into the entire week ahead. Therefore, as Shabbos departs, a person must yearn for Hashem Yisbarach and entreat that the coming weekday deeds not separate him from Him — declaring his devotion in advance, like a mesiras moda'a lodged before the deed, so that the kedushah of Shabbos carries through into all his weekday avodah.