At the end of Yitzchak’s life, the Torah tells us, he lost his eyesight. This, of course, sets the stage for Yaakov to pose as his brother Esav, gaining the beracha which ought to have been his anyway. In this sense, we usually think of the blindness of Yitzchak as connected to the rest of the pasuk (Bereishit 27:1) and the ensuing narrative: Yitzchak is blind, so he chooses Esav over Yaakov because the blindness affects his perception in this matter as well.
However, Rashi’s comments on Yitzchak’s blindness tie it into the preceding pesukim describing Esav’s heathen wives and the misery they caused his parents. Rashi explains that Esav’s wives practiced idolatry in their home, to Yitzchak and Rivka’s great consternation. He gives three explanations for how Yitzchak lost his sight. The first of these is that he was blinded by the smoke of the offerings these women made to their idols. Siftei Chachamim wonders why Yitzchak was blinded by the pagan offerings but Rivka was not, first suggesting that she might have grown accustomed to such things while growing up in the company of her father and brother. In the end, he concludes that Yaakov’s eyes had already been weakened by the smoke of the fire at the Akeda, when he was almost sacrificed upon the altar.
R’ Eliyahu Mizrachi does not accept this approach, and he understands the connection of blindness with idolatry as allegorical, not unlike the other connection we made above to choosing the wrong brother. Mizrachi says that the foul pagan ceremonies of the wives of Esav in the home of Yitzchak and Rivka caused the Divine Presence to abandon them. Thus, as a result of this idolatry, Yitzchak lost his power of prophecy and so became spiritually blinded.
Maharal in Gur Aryeh takes a slightly different approach to understanding Rashi on this pasuk. He ties it back to the Akeidah as Siftei Chachamim did, but he understands this more on a spiritual level like Mizrachi. Of course, we don’t usually think of Avraham having lit the fire on the mizbe’ach before slaughtering the korban – Yitzchak. Also, the second answer of Rashi, brought from the Midrash, seems more apocryphal and harder to accept as a literal explanation of Yitzchak’s condition. According to this view, malachim in heaven were crying over the Akeidah and some of the tears fell into Yitzchak’s eyes.
Maharal says that when Yitzchak was brought as a korban, his own status changed, elevating him to a higher level of kedusha. He was no longer just some person, even a very righteous one – he had become a designated offering and a part of the Divine Service. When this happened, his vision was also elevated and made more sensitive to refined and holy things. After the Akeidah, Yitzchak no longer saw with normal human vision the objects of everyday experience. His eyes had become spiritual organs by means of which he felt and experienced the true essence of all things in the world, good and bad. The enormity of the corruption of the idolatrous practices of the wives of his firstborn was enough to destroy his faculty of vision altogether. Yitzchak’s holy eyes were not able to behold the terrible acts of these women, so they went blind instead.
Rabbi Avraham Abulafia in his commentary on Bereishit entitled Mafte’ach HaChochma notes that our entire parsha is an allegory for the struggle between good and evil inclinations in a single body. The twins literally wrestle inside of Rivka, but Yitzchak also has to come to terms with his disappointment in what Esav becomes. This is a significant factor in his blindness, which Abulafia points out only applies to his vision – and his decision about whom to bless. Yitzchak is not fooled by the voice of Yaakov, by the feel of his hands, or by the feast that Rivka prepared for him. Yitzchak preferred to believe that if Esav was only supported fully – if he was strengthened by the beracha that Yitzchak had prepared for him – then in the end he would also turn out to be good and righteous. In spite of this, we learn how Esav was a torment to his parents. Rav Avraham Abulafia says that this last blow was the cruelest, because it disrupted Yitzchak’s spiritual sensitivity, his faculty of prophecy, to such an extent that had it not been for the intervention of Rivka, he would have given the beracha to the wrong son in the end.
Nevertheless, there are also certain guardrails built into Creation to limit such errors. For example, Yitzchak gives Yaakov Avraham’s blessing from Hashem that “Those who curse you will be accursed.” But he doesn’t then turn around to curse Esav – nor can he revoke Yaakov’s beracha and change it to a curse once he realizes the deception. That same faculty of prophecy is necessary to curse just as it was to bless. This is also why, when he most earnestly wants to, Bilaam is not able to curse the Children of Israel. We, and especially the tzaddikim among us, have the power to make moral choices about the people with whom we interact, and we might even find it in ourselves to bless or to curse. But ultimately, we cannot confer blessing on someone wholly unsuited to receive the blessing and we cannot curse those who have been blessed by G-d.