Yirah born from ahavah is true

תולדות יצחק בן אברהם אברהם הוליד את יצחק.

"These are the generations of Yitzchak, son of Avraham; Avraham fathered Yitzchak."

The Sefas Emes begins from the verse's seeming repetition — Yitzchak son of Avraham, and Avraham fathered Yitzchak — which invites deeper interpretation.

כל מעשה אבות סי' לבנים כי לא עשה שום מעשה שלא יהי' לטובת כל בנ"י לדורות.

Every deed of the Avos is a sign for the children, for they did no act that was not for the benefit of all Bnei Yisrael for all generations.

Invoking the principle "ma'aseh avos siman labanim," nothing the Avos did was for themselves alone — every act laid down a spiritual inheritance for their descendants.

ואיתא בספרים כי יראה הבא מכח אהבה היא יראה של אמת.

And it is brought in the sefarim that yirah (awe) that comes from the power of ahavah (love) is the true yirah.

The seforim teach that the highest, most authentic fear of Hashem is one that grows out of love for Him, rather than fear standing on its own.

וז"ש יצחק בן אברהם וכ' רש"י עדות יש שאברהם הוליד כו'.

And this is the meaning of "Yitzchak son of Avraham," and Rashi writes: there is testimony that Avraham fathered Yitzchak.

Rashi notes the verse testifies that Yitzchak truly issued from Avraham; the Sefas Emes reads this as Yitzchak's trait of yirah issuing directly from Avraham's trait of ahavah.

פי' זה היראה שבא מכח אהבה היא מבוררת בלי תערובות שקר.

The meaning is: this yirah, which comes from the power of ahavah, is pure, without any admixture of falsehood.

Yitzchak's awe, born of Avraham's love, is wholly clarified and genuine, untainted by the false motives that can creep into fear alone.

ופי' יראה הנ"ל הוא שיהי' יראה לאדם פן ינתק מדביקות אהבתו להש"י והוא אהבת אמת:

And the meaning of the aforementioned yirah is that a person should fear lest he be severed from the devekus of his love for Hashem — and this is true love.

This refined yirah is not dread of punishment but the loving anxiety of one who fears, above all, losing his cleaving attachment to Hashem; such fear is itself the mark of true ahavah.

Summary: Every deed of the Avos is a sign and inheritance for their descendants. The verse "Yitzchak son of Avraham" expresses how Yitzchak's defining trait of yirah issued from Avraham's trait of ahavah — for the truest yirah is one born of love. Such fear is pure and untainted, for it is not dread of punishment but the loving dread of being severed from one's devekus to Hashem, which is itself the hallmark of genuine ahavah.