The Torah tells us that Yitzchak was blind in his old age. According to one explanation provided by Rashi, G‑d caused this to happen “in order to enable Yaakov to take the blessings.”
Now, to say that blindness is debilitating is an understatement, as Rashi comments, “Because Yitzchak’s eyes had become dim and he was confined to his house... he was as though dead.”
Nevertheless, because Yitzchak planned to bestow the greatest blessings upon Eisav, not knowing the full extent of his wickedness, G‑d caused him to become blind in order for Yaakov to successfully disguise himself as Eisav and receive the blessings instead.
Consider this: Yitzchak was 123 years old at the time of the blessings, and he lived until the age of 180. So for 57 years Yitzchak suffered from blindness, confined to his house “as though dead,” all because he was unaware of Eisav’s wickedness and therefore desired to bless him. Was this really necessary? Why didn’t G‑d simply inform Yitzchak that Eisav wasn’t worthy of the blessings, just as He communicated many other things to him?
(Moreover, Yitzchak already had suspicions about Eisav. He disapproved of Eisav’s wives, and he was aware that Eisav did not have the praise of G‑d on the tip of his tongue. So why did G‑d not reveal the whole truth about Eisav, instead of causing Yitzchak to be blind for the last 57 years of his life?)
From here we see the extent to which one must be willing to go in order to avoid speaking negatively about another Jew. G‑d deemed it preferable to cause Yitzchak to be blind for over five decades rather than to tell him lashon hara about the wicked Eisav!
If this is true concerning Eisav, how much more careful must we be when speaking about our fellow Jews, the most sinful of whom are certainly not nearly as wicked as Eisav was!
—Likkutei Sichos vol. 15, pp. 215–216
