Wholehearted Acceptance Enables Rectification
אא"ז מו"ר ז"ל הגיד בפסוק כי אתם באים כו'
My grandfather, my master and teacher of blessed memory, expounded on the verse "For you are coming" (Bamidbar 33:51, regarding crossing the Yarden into Eretz Yisrael).
The Sfas Emes opens by citing a teaching of his grandfather, the Chiddushei HaRim, on the verse about Bnei Yisrael coming into Eretz Yisrael.
כי צריך האדם לקבל על עצמו להיות מיוחד להשי"ת כרצונו עד שלא יהי' נשכח ממנו אף רגע אחד
For a person must take upon himself to become wholly dedicated to Hashem according to His will, to the point that He should not be forgotten from him for even a single moment.
A person's job is to commit himself completely to Hashem's will, so totally that he never forgets Him for even a moment.
אף שיודע האדם כי איננו במדריגה זו
Even though a person knows that he has not reached this level,
This commitment is demanded even from one who honestly recognizes he is far from actually living on that lofty level.
מכל מקום הקבלה והרצון צריך להיות עצהיו"ט
nevertheless, the acceptance and the desire must be with the full essence of his being.
What counts is that the inner acceptance and yearning come from the deepest core of who he is.
וזה מועיל שיוכל לעשות דבר מה עכ"פ עכ"ד
And this is effective, that he will be able at the very least to accomplish something — that is, the words of my grandfather.
Even a commitment one cannot fully live up to is valuable, because it empowers a person to at least accomplish part of the goal — and these were the grandfather's words.
[כמדומה לי שכן אמר ואפשר בשינוי לשון קצת]. ונראה להוסיף כי הי' גלוי וידוע להשי"ת שישאירו מכנענים
[It seems to me that this is what he said, though perhaps with some slight change of wording.] And it appears fitting to add that it was revealed and known before Hashem that they would leave over some of the Canaanites,
The Sfas Emes adds his own point: Hashem already knew in advance that Bnei Yisrael would fail to drive out all the Canaanites.
ואעפ"כ הי' רצונו ית' שיקבלו עליהם את זה לעקר אותם מכל וכל
and even so, it was His blessed will that they take this upon themselves — to uproot them entirely and completely.
Yet Hashem still wanted them to accept upon themselves the full obligation to root out the Canaanites entirely.
וכן כ' חז"ל שקבלו עליהם כשעברו הירדן והי' זה עצה אף שישאירו יוכלו לתקן זאת כמו שיהי' לעתיד הכל מתוקן בעזרת השי"ת
And so too the Sages wrote that Bnei Yisrael accepted this upon themselves when they crossed the Yarden; and this was the counsel: that even if they would leave some over, they would be able to rectify this, just as in the future to come everything will be set right with the help of Hashem,
The Sages teach that Bnei Yisrael took on this acceptance at the crossing of the Yarden; the very acceptance was the strategy, since even a partial failure could later be repaired, just as everything will ultimately be perfected in the future geulah.
ע"י הקבלה שקבלו עליהם כראוי כנ"ל:
through the acceptance that they took upon themselves in the proper manner, as explained above.
All of this rectification flows from the wholehearted acceptance they undertook in the proper way, as explained.
Summary: The Sfas Emes, building on a teaching of his grandfather the Chiddushei HaRim regarding Bnei Yisrael's entry into Eretz Yisrael, teaches that every person must take upon himself to be utterly devoted to Hashem's will, never forgetting Him for even a moment. Even one who knows he cannot truly reach this level must still make this acceptance and yearning from the depths of his being, for such a commitment empowers him to accomplish at least something. He then adds that Hashem knew in advance that Bnei Yisrael would not drive out all the Canaanites, yet still willed that they accept the full obligation to uproot them completely. The acceptance itself, undertaken at the crossing of the Yarden, was the counsel: precisely because of this wholehearted commitment, any shortcoming can ultimately be rectified, just as everything will be set right in the future geulah with the help of Hashem.