Three Avos Three Levels
והי' עקב תשמעון כו' ושמרתם ועשיתם
"And it shall be, because (eikev) you will hearken... and you shall guard and you shall do" (Devarim 7:12).
The Sfas Emes opens with the pasuk that promises blessing in the merit of hearkening to, guarding, and performing the mitzvos.
לתת שכר לשמיעה ושמירה ועשי'
This is to grant reward for hearing, for guarding, and for doing.
He notes that the pasuk lists three distinct deeds for which reward is given: hearing, guarding, and doing.
והם ג' מדרגות
These are three levels.
These three deeds are not interchangeable but represent three ascending stages in a person's avodah.
השמיעה היא הקבלה בלב
Hearing is the acceptance in the heart.
The first stage, hearing, refers to inwardly accepting the word of Hashem in one's heart.
אח"כ השמירה ועשי'
Afterward come guarding and doing.
Once that acceptance takes root, the further stages of guarding and doing can follow.
והם בחי' ג' אבות
And these correspond to the aspect of the three Avos.
The Sfas Emes maps these three stages onto the three Avos, each of whom embodied one of them.
באברהם אע"ה נאמ' שמעי בת שהי' הראשון לשמוע דבר ה' ובחי' בכל לבבך
Regarding Avraham Avinu it is said, "Hear, O daughter" (Tehillim 45:11), for he was the first to hear the word of Hashem, and this is the aspect of "with all your heart."
Avraham is the dimension of hearing, since he was the first to hear and accept Hashem's word, paralleling "with all your heart" of Krias Shema.
ושמירה נגד יצחק והיא בכל נפשך
And guarding corresponds to Yitzchak, and it is "with all your soul."
Yitzchak is the dimension of guarding, paralleling "with all your soul" in Krias Shema.
רמז לדבר ושמרתם את נפשותיכם כי שמירה בנפש
A hint to this matter is "and you shall greatly guard your souls" (Devarim 4:15), for guarding is in the soul.
He brings a supporting allusion from the pasuk warning to carefully guard our souls, showing that the avodah of guarding is bound up with the neshamah.
ועשיתם נגד יעקב אע"ה בחי' בכל מאודך:
And doing corresponds to Yaakov Avinu, the aspect of "with all your might."
Yaakov is the dimension of doing, paralleling "with all your might," completing the three-fold structure of hearing, guarding, and doing through the three Avos.
Summary: The Sfas Emes takes the opening pasuk of the parsha, which speaks of hearkening, guarding, and doing, and reads these as three ascending levels of avodah. Hearing is the inner acceptance of Hashem's word in the heart, after which guarding and doing follow. He aligns these three levels with the three Avos: Avraham is hearing, paralleling "with all your heart," for he was the first to hear the word of Hashem; Yitzchak is guarding, paralleling "with all your soul," as guarding is rooted in the neshamah; and Yaakov is doing, paralleling "with all your might." In this way the threefold language of the pasuk corresponds to the three Avos and to the three dimensions of devotion expressed in Krias Shema.