Toldot (“Generations”) opens with the births of Isaac and Rebecca’s twins, Jacob and Esau. Esau sells his birthright to Jacob in exchange for soup. Isaac and Rebecca travel to Gerar, where Isaac makes a peace treaty with King Abimelech. Isaac gives Jacob the blessing meant for Esau, and Jacob runs away to his uncle Laban.
וַיְהִי֙ כִּֽי־זָקֵ֣ן יִצְחָ֔ק וַתִּכְהֶ֥יןָ עֵינָ֖יו מֵרְאֹ֑ת וַיִּקְרָ֞א אֶת־עֵשָׂ֣ו ׀ בְּנ֣וֹ הַגָּדֹ֗ל וַיֹּ֤אמֶר אֵלָיו֙ בְּנִ֔י וַיֹּ֥אמֶר אֵלָ֖יו הִנֵּֽנִי׃
When Isaac was old and his eyes were too dim to see, he called his older son Esau and said to him, “My son.” He answered, “Here I am.”
ותכהין HIS EYES WERE DIM through the smoke raised by these women in offering incense to idols (Midrash Tanchuma, Toldot 8). Another explanation is: When Isaac was bound upon the altar and his father was about to slay him, at that very moment the heavens opened, the ministering angels saw it and wept, and their tears flowed and fell upon Isaac’s eyes which thus became dim (Genesis Rabbah 65:5). Another explanation is: They became dim just in order that Jacob might receive the blessings (Genesis Rabbah 65:8).
(13) And I declare to him that I sentence his house to endless punishment for the iniquity he knew about—how his sons committed sacrilege at will—and he did not rebuke them.
(טו) וְעֵלִ֕י בֶּן־תִּשְׁעִ֥ים וּשְׁמֹנֶ֖ה שָׁנָ֑ה וְעֵינָ֣יו קָ֔מָה וְלֹ֥א יָכ֖וֹל לִרְאֽוֹת׃
(15) Now Eli was ninety-eight years old; his eyes were fixed in a blind stare.
(22) And the LORD God fashioned the rib that He had taken from the man into a woman; and He brought her to the man.
The Gemara provides another lesson from the story of Abraham and Abimelech. And Rabbi Yitzḥak says: The curse of an ordinary person should never be regarded as light in your eyes, for Abimelech cursed Sarah and it was fulfilled in her descendant. The curse on Sarah is as it is stated: “Behold, it is to you a covering of the eyes” (Genesis 20:16), meaning that he said to her: Since you concealed your status from me and you did not reveal that Abraham is your husband, and you caused me this suffering, may it be God’s will that you should have children with covered eyes. And this curse was fulfilled in her descendant, as it is written: “And it came to pass, that when Isaac was old, and his eyes were dim, so that he could not see” (Genesis 27:1).
Noam Zion
Isaac's blindness had to have been willful. Isaac, who had seen all too clearly the results of his father's "vision," chose, when his turn came, to "close his eyes" to Esau's intermarriage, despite the pain it caused him. He refused to cut off the child who loved him.
(34) When Esau was forty years old, he took to wife Judith daughter of Beeri the Hittite, and Basemath daughter of Elon the Hittite; (35) and they were a source of bitterness to Isaac and Rebekah.
Genesis Rabbah 65:10
R. Eleazar ben Azaria taught: From seeing the evil deeds of wicked Esau. For the Holy One said: "Shall Isaac go out into the marketplace and hear people say, 'This is that scoundrel's father'? I shall therefore dim Isaac's eyes so that he will stay home."
Or the phrase "from seeing" is to be explained by the tale of a distinguished man who had a beautiful and well-appointed reception room, next to which his neighbors used to burn stubble and straw, sending smoke in through the window. The man felt constrained to seal the window. Likewise, while Esau's wives worshiped idols, Isaac saw them and was so greatly distressed that at once his eyes grew dim.
Archbishop Rembert Weakland, O.S.B. (Archbishop of Milwaukee)
The image of Isaac's blindness reminds us that God is in control, not we ourselves. Out of circumstances that seem wrong to us, God can and does bring into being the good He (sic) wishes. His ways are not our ways; we have to keep learning and relearning that. What might seem to us a lack of justice would presuppose that we had rights to God's love and grace, and this is a way of saying: Not so.
Rabbi Burton L. Visotzky (1991)
It was a blindness that left Isaac in darkness deeper than that which plagued Egypt. Isaac, who as a youth was blind to his half-brother's designs, who as he grew was blind to his father's dangerous devotion to God, who as he married was blind to the corruptions of his brother-in-law, who as he fathered was blind to the petty flatteries of his sons, who as he aged was blind to his wife's preference of one son and her schemes to advance him over the other - truly Isaac could not see. It was a total blindness, as only angel tears can bring.
Midrash Rabbah 65:10
When Isaac lay upon the altar, about to be sacrificed by his father, the angels wept, and their tears fell upon his eyes, and there they remained and weakened his sight.
Freema Gottleib (from The Lamp of God: A Jewish Book of Light (1989)
Isaac was said to have been blinded not only by the flames of the sacrifice of which he was almost a part, but by the Shekhinah (the divine presence) that appeared to him on that occasion. Some types of darkness and blindness are indicative of an excess of light.
(20) But,” He said, “you cannot see My face, for man may not see Me and live.”