The Sefas Emes explains that actually this equation means more than meets the eye. It is more than a clarification of Yitzchak’s DNA. It goes to the very core of the foundations upon which the future Klal Yisrael was to be built. Avraham and Yitzchak had divergent approaches to their avodas, service, to Hashem. Avraham had boundless love for the Almighty that literally overflowed from him. This love catalyzed him to become a baal chesed, directing him outward through acts of loving-kindness. He taught monotheism to the masses, imbued them with the ethics of the Torah and planted an eishel, which was either an inn or an orchard, as a means of educating travelers when they stopped to rest. His acts of chesed did not rest, even when he was recuperating from his Bris Milah. He sat at the door of his tent waiting, yearning to reach out to any passersby.
Yitzchak’s avodah was not love-based; rather, the second Patriarch’s fear of Hashem, concretized during the Akeidas Yitzchak, made him draw inward, meticulously introspecting each action before executing it, in order to determine that the consequences of his action would befit a servant of Hashem. These two paths – love versus fear – are, under normal circumstances, mutually exclusive. In Judaism, however, they have the opportunity to achieve unity. True yiraas Shomayim, fear of Heaven, is to be in awe of the Almighty. This is a byproduct of a deep sense of love that one has for Hashem. This applies vice versa, with each emotion – fear and love; love and fear – completing the other.
Another form of fear, however, is inconsistent with love – fear of punishment, which is essentially a self-centered fear. This is the type of fear prevalent in the nations of the world. In his encounter with Avraham, Avimelech exhibited this type of fear. Thus, when the scoffers claimed that Yitzchak was the progeny of Avimelech, they were intimating that his fear was none other than fear of punishment. When the Torah attests to Avraham’s fathering Yitzchak, it is saying that Yitzchak was the product of the attribute of love. Yitzchak’s pure fear of Hashem was the result of – and rooted in – his intense love for, and awe of, the Creator.
The Sefas Emes takes this thesis to the next level. While Yitzchak’s fear of Hashem had its source in his love of Hashem, he still lacked the perfect synthesis of these two traits. Hashem’s blessing to Yitzchak’s seed required the merit of Avraham. This is to be derived from the following pesukim: “I will multiply your seed like the stars of the sky since Avraham listened to My voice” (Bereishis 26:4-5); “I will bless you and multiply your seed for the sake of Avraham, My servant” (Ibid 26:24). Clearly, Avraham is a primary component in the blessing of Yitzchak’s seed.
This is to be understood in the following manner: Chazal teach that Hashem originally sought to create the world through Middas HaDin, the Attribute of Strict Justice, but He saw that unless it was tempered with Divine Mercy, the world had no chance of survival. The foundation of Klal Yisrael also calls for an alliance between these two attributes. Love can become tainted. For this, Avraham needed Yitzchak’s pure fear to maintain its pristine essence. Yitzchak’s Din required bolstering from the merit of Avraham to give it continued existence among future generations. The two middos working in tandem formed the prefect base upon which to build an enduring Jewish nation.