The Sforno comments, that although the Zechus Avos (merit of our ancestors) is a fundamental concept of Judaism, it is only invoked regarding Yitzchok. Among the three Avos, Avrohom had to develop his own merits, while Yaakov like his grandfather, proclaimed the name of Hashem and taught it to others. Yitzchok however, being the Olah Temimah “perfect sacrifice” was very special and practiced his faith in private and never had the opportunity to instill and imbue others with the belief in Hashem. He therefore needed his ancestors merit for his own preservation. This was only before he was inspired to call upon the name of Hashem. However, once he called upon the name of Hashem, he was worthy on his own to be blessed by Hashem. As it is written, Avimelech the king of Gerar came to Yitzchok and said, “we saw that Hashem was with you, and you are now blessed by Hashem“. After this he was no longer plagued by the hardships of envy and quarrels, which he had previously experienced.
It may be noted from Sforno’s commentary that an integral part of the mitzvah of Torah study, is the teaching of Torah to others. This point is clearly indicated in our daily prayer of Ahava Rabba where we ask “to instill understanding in our hearts, to learn Torah, and to teach, safeguard and perform“. Teaching Torah to others is an essential prerequisite for the fulfillment of the mitzvah of Torah study.
