Commento su Genesi 27:33

ויחרד [AND ISAAC] TREMBLED — Explain it as the Targum renders it ותוה, which means he was perplexed. The Midrashic explanation (Midrash Tanchuma, Toldot 11) is that he saw Gehinnom opening beneath him (Esau).

AND ISAAC TREMBLED VERY EXCEEDINGLY, AND SAID, WHO THEN IS HE THAT HATH TAKEN VENISON AND BROUGHT IT TO ME, AND I HAVE EATEN OF ALL BEFORE THOU COMEST AND HAVE BLESSED HIM? YEA, AND HE SHALL BE BLESSED. It is not natural for a person who just trembled violently and complained, “Who was it that subtly made me bless him?” to conclude his complaint by immediately saying, Yea, and he shall be blessed! Rather, it would have been proper that he curse him! Moreover, Esau would then complain to his father, saying, “But why do you bless him now, my father?” And how would Esau believe his father that it was originally done through subtlety²²⁹Verse 35 here. when he saw that he was now blessing him willingly!
The correct interpretation appears to me to be that it is in the present tense.²³⁰The word yihyeh, generally understood as a future tense — and he shall be blessed — is here to be understood as a present tense, as explained below in the text. Isaac is saying, “Who then is he that hath hunted venison, who could have beguiled me so that I should bless him and that he should remain blessed under all circumstances for I knew that he is a blessed one?” Or it may be that the expression, Yea, and he shall be blessed, means “against my will, since it is impossible for me to transfer the blessing from him.” From the moment he blessed him, Isaac knew by Ruach Hakodesh²³¹See above, Note 90. that his blessings indeed rested upon Jacob. This then is the reason for his violent trembling for he knew that his beloved son Esau had lost his blessing forever. This also is the explanation for his saying, Thy brother came with subtlety,²²⁹Verse 35 here. meaning that after he said, Who then is he etc. he realized that Jacob had been the one who came before him to receive the blessing for it would have been impossible for the blessing to rest on any but his offspring, [and, as mentioned above, Isaac knew by Ruach Hakodesh that the blessing had taken effect. Hence he was sure that it was Jacob who had come before him.]

ויחרד יצחק, he was upset at having found hair on the smooth part of Yaakov’s neck.