I would like to present my own explanation for the reason Yaakov Avinu chose to formulate the mitzvah of Krias Shema in terms of hearing rather seeing. He foresaw via “ruach hakodesh” the inherent danger posed by the ministering angel of Eisav, the yetzer hara—that it disguises an aveirah as a mitzvah. As we learned above, this prompted him to pray: “Save me, please, from the hand of my brother, from the hand of Eisav.” Therefore, he instituted that Yisrael would accept upon themselves “ohl malchus shamayim” in terms of hearing: "שמע ישראל" –-“Hear, O Yisrael.” He wanted all future Jews to listen and heed the words of the sages of the Torah led by Rabeinu HaKadosh, his “nitzotz.” Thus, they would be able to discern the proper, upright path to follow—to make HKB”H their king and acknowledge His oneness: "ה' אלקינו ה' אחד".
This explains magnificently the Jewish custom to cover the eyes when reciting the passuk: "שמע ישראל ה' אלקינו ה' אחד". The source for this minhag is found in the Shulchan Aruch (O.C. 61, 5): They customarily place their hands over their faces when reciting the first passuk so as not to look at something else that will prevent one from focusing. In Sha’arei Teshuvah (ibid. 3), he provides the following clarification: When the Shulchan Aruch writes “over their faces,” he means over their eyes. And this is also what he (the Arizal) wrote in Pri Eitz Chaim: He should close (cover) his eyes with his right hand.
Let us explain the matter in keeping with our current discussion. When a person relies on what he perceives with his own eyes to decide on a proper course of action, there is a significant danger that the yetzer hara will mislead him to mistakenly perceive an aveirah as a mitzvah. Therefore, we cover our eyes so as not to rely solely on our mind’s eye—the perception of our intellect. Thus, when we cover our eyes, we accept upon ourselves “ohl malchus shamayim” with intense emotion and reverence based on proper hearing: "שמע ישראל ה' אלקינו ה' אחד".
We now have cause to rejoice! We have been enlightened! We can now comprehend why Rabeinu HaKadosh, the “nitzotz” of Yaakov Avinu began Torah she’b’al peh with the mitzvah of Krias Shema. He, too, just like his predecessor, feared that man would go astray following the yetzer hara that portrays an aveirah as a mitzvah and a mitzvah as an aveirah. It was precisely for this reason that he teaches us this lesson in the Mishnah: “Rebbe says: Which is the proper path that a man should choose for himself? Whatever is a credit (“Tiferes”) to himself and earns him the esteem (“Tiferes”) of fellow men.”
For this same reason, he began Torah she’b’al peh as follows: "מאימתי קורין את שמע בערבית"—with the mitzvah of Krias Shema of Arvis. He wished to teach us that when a person feels confused and uncertain—like the darkness of the night—and does not know which path to choose, he should accept upon himself “ohl malchus shamayim” with the words: "שמע ישראל". In other words, he should listen to and heed the teachings of the sages of the Torah. By doing so, he will merit unifying the name of HKB”H: "ה' אלקינו ה' אחד".
