Lasting blessing requires chesed over din

ונתתי לזרעך כו' עקב אשר שמע אברהם בקולי כו'.

"And I will give to your seed… because (eikev) Avraham hearkened to My voice…"

Hashem confirms the promise of the land to Yitzchak's descendants, but bases it on Avraham's merit rather than Yitzchak's own.

וקשה הלא איתא כל אחד מאבות כדאי לעצמו ולמה תלה לו ה' ית' בזכות אברהם.

And this is difficult: surely it is taught that each of the Avos is worthy in his own right — so why did Hashem make it depend on the merit of Avraham?

Since Yitzchak too was a complete tzaddik with his own merit, why anchor the promise specifically in Avraham's zechus?

אבל הענין הוא כי המתנה לדורות לזרע ישראל א"א לתלות ביצחק שהיא מדה"ד.

But the matter is that a gift meant for all generations of the seed of Yisrael cannot be made dependent on Yitzchak, who is the attribute of strict judgment (middas ha'din).

Yitzchak embodies din, exacting justice — and an everlasting gift to future generations cannot rest on so demanding a standard.

ורצה להנהיג הכל על קו הדין ממש.

And he [Yitzchak] wished to conduct everything strictly along the line of judgment.

Yitzchak's way was to run the world by precise, unbending justice.

וכבר ראה הקב"ה שאין העולם מתקיים ע"פ מדה"ד.

But Hashem had already seen that the world cannot endure according to the attribute of strict judgment.

As Chazal teach about creation, a world run on pure din cannot survive; it requires chesed and rachamim.

לכן תלאו הכתוב במדת אברהם.

Therefore the pasuk made it depend on the attribute of Avraham.

Avraham embodies chesed (lovingkindness), the attribute on which an enduring world can stand.

הגם כי הכל במשפט.

Even though everything is [still] through judgment (mishpat).

This does not abolish justice — there is still a din at work, but of a different character.

אבל יש משפט שדנין האדם אם ראוי לעשות עמו חסד.

But there is a kind of judgment in which a person is judged as to whether he is worthy that chesed be done with him.

Even chesed involves a judgment — Hashem assesses whether a person deserves to receive kindness.

וזה הוא המשפט בבחי' החסד שבו מתנהג העולם.

And this is the judgment within the aspect of chesed, by which the world is conducted.

The world runs on this blended mode: a justice that operates inside the framework of kindness.

והנה מתנה זו נתן לו המקום בחסדו ית' והגם שזכה במדת הדין ג"כ רצה הקב"ה לתת לו במדת החסד ולכן תלאו במעשה אברהם והבן.

Now, Hashem gave him this gift in His chesed; and although [Yitzchak] was worthy even by the attribute of judgment, Hashem wished to grant it to him through the attribute of chesed — and therefore He made it depend on the deed of Avraham; understand this.

Yitzchak deserved the gift even on the strict accounting of din, but Hashem chose to convey it through chesed, so as to set it on a footing that could last for all generations.

ואפשר הי' זה הטעם שהזמין הבורא ית' להיות ברכת יעקב מאביו שלא מדעתו.

And perhaps this was the reason the Creator arranged that Yaakov's blessing from his father should come about without [Yitzchak's full] awareness.

This same principle may explain why Hashem orchestrated that Yitzchak bless Yaakov while thinking he was blessing Esav.

כי רצון יצחק הי' לברכו ע"פ מדה"ד כמ"ש רש"י ז"ל ויתן לך האלקים בדין כו'.

For Yitzchak's intention was to bless according to the attribute of judgment, as Rashi explains on "And may Elokim give you" — "in justice…"

The Divine Name Yitzchak used (Elokim) signals din; he meant to confer the blessing on the strict terms of justice.

אך דינו של יצחק א"א להתקיים בו העולם.

But the judgment of Yitzchak is such that the world cannot endure by it.

A blessing given on Yitzchak's exacting standard of din could not provide a lasting foundation.

אכן בהיותו סבור כי הוא עשו ובלי ספק ידע יצחק כי גדלה מעלתו של יעקב מעשו רק שרצה לברך הבכור.

However, while he supposed it was Esav — and surely Yitzchak knew that Yaakov's stature was greater than Esav's, only that he wished to bless the firstborn —

Yitzchak was well aware of Yaakov's superiority; he intended the bechor's blessing, in strict justice, for Esav as the firstborn.

וידוע כי לפי מדרגת הנשפט הוא המשפט.

And it is known that the judgment is according to the level of the one being judged.

The standard of justice applied to a person is calibrated to his spiritual stature.

והמשפט של הצדיק הוא בוודאי ביותר דקדוק כמ"ש ז"ל מדקדק עם הצדיקים כחוט השערה.

And the judgment of the tzaddik is surely with greater exactitude, as Chazal said: "He is exacting with the righteous to a hair's breadth."

Because din is measured by the recipient's level, a blessing in strict justice falls far more severely upon a lofty tzaddik like Yaakov than upon Esav.

ונמצא ברכתו שבירך לעשו כפי דעתו במדה"ד.

It emerges that the blessing he gave, as he thought, to Esav according to the attribute of judgment —

The blessing, framed in din and intended for Esav,

הרי הוא ליעקב במדת חסד ורחמים והבן.

is, for Yaakov, [received] through the attribute of chesed and mercy; understand this.

Because the same strict measure is far gentler when applied to one of lower stature, a blessing of "din for Esav" became, when it landed on the loftier Yaakov, effectively a blessing of chesed and rachamim.

והי' כ"ז לטובתינו אנחנו זרע יעקב כי יעקב אע"ה בעצמו בלי ספק זכה בדין ג"כ.

And all this was for our benefit, we the seed of Yaakov, for Yaakov Avinu himself surely merited even by judgment.

Yaakov personally would have withstood strict din; the chesed arrangement was needed for the sake of his descendants throughout the generations.

וז"ש לאמו הן עשו אחי איש שעיר ואנכי איש חלק.

And this is what he said to his mother: "Behold, Esav my brother is a hairy man, and I am a smooth man."

The Sefas Emes rereads Yaakov's words to Rivkah as more than a practical worry about the disguise.

לפי הנ"ל הפי' שאיך יקח הוא ברכה המיוחדת לעשו אבל הי' לטובת בניו אחריו כנ"ל:

According to the above, the meaning is: how could he take a blessing designated [in strict justice] for Esav? — but it was for the benefit of his children after him, as explained.

Yaakov hesitated to seize a blessing framed for Esav's measure, but in truth Hashem arranged it so that this very blessing would reach Yaakov as chesed and endure as a gift for all his descendants.

Summary: The promise of the land is anchored in Avraham (chesed) rather than Yitzchak (din), because an everlasting gift to future generations cannot rest on strict judgment, which the world cannot endure. The same principle illuminates Yaakov's blessing: Yitzchak intended a blessing of din for the firstborn Esav, but since strict justice is measured by the recipient's stature, that very blessing, when received by the loftier Yaakov, became one of chesed and rachamim — all arranged for the lasting benefit of Yaakov's descendants.