In Parashat Toledot, Ya’akov and Eisav are born. The Pasuk states (BeReishit 25:27-28), “VaYigedalu HaNe’arim VaYehi Eisav Ish Yodei’a Tzayid Ish Sadeh VeYa’akov Ish Tam Yosheiv Ohalim. VaYeEhav Yitzchak Et Eisav Ki Tzayid BeFiv VeRivkah Ohevet Et Ya’akov,” “The lads grew up and Eisav became one who knows hunting, a man of the field, but Ya’akov was a wholesome man, dwelling in tents. Yitzchak loved Eisav for game was in his mouth, but Rivkah loved Ya’akov.”
Rashi (25:27 s.v. Yodeiya Tzayid) states that Eisav would capture and trick his father with his mouth. He would ask him, “Father, how do you take Ma’aseir from salt and straw?” Eisav knew that Ma’aseir is only taken from fruits fit for human consumption, which excludes both salt and straw. Yitzchak, however, mistakenly thought that Eisav was careful about Mitzvot. Again, Rashi (25:28 s.v. Ki Tzayid BeFiv) cites the Midrash that “BeFiv” refers to the mouth of Esav, because Esav would “capture” and trick Yitzchak with his words.
The Tiferet Yechezkel observes that Eisav’s questions about Ma’aseir were clearly foolish. How is it possible that Yitzchak was tricked by these? Did Yitzchak really not know the truth about Eisav? Further, Rivkah was told when she was pregnant and went to inquire about strange happenings in her stomach that she would have two nations - one would be wicked and one would be wholesome (5:23). How could Yitzchak have ignored this so blatantly? Could he truly have been tricked into loving him so much?
It is worthwhile to look at a psychological profile of Yitzchak. Yitzchak has a strong commitment to and belief in Hashem, as evidenced by his role in the Akeidah. After he realizes what was happening, that he was being led to his death, he was still confident that everything would be all right (Rashi 22:8 s.v. Yir’eh Lo HaSeh). Furthermore, Yitzchak was not confused as some people mistakenly think he was. He was very aware of situations. From the supremely challenging mission of the Akeidah to Eisav's true character and destiny, Yitzchak was always keenly aware of the truth.
Let us consider what an average person would do if he was told with certainty that his son would be evil. Realizing it was a predestined conclusion, how would he feel and respond? He would obviously feel sad, depressed, and likely hopeless. Yitzchak was in such a situation. But what did he do? He was the ultimate optimist and loving father who looked for the best in his son and the situation, and remained hopeful and optimistic that things would turn out positively. He genuinely believed that there was still a chance that Eisav would turn out all right. He tried his best to nurture Eisav, hoping to help make a difficult situation a good one. He did everything he could and looked for every sign, even the smallest indication of hope.
The Tiferet Yechezkel maintains that when Eisav posed those foolish questions, Yitzchak wasn’t tricked into thinking that Eisav was concerned with Mitzvot and therefore loved him more. Yitzchak never gave up hope regarding his son. To Yitzchak, those questions were a possible sign of a spark in Eisav's soul, which could be nourished and fanned with extra love, care, and optimism. He wasn't a fool or in a fog. He was simply an optimist and a loving father.