Charles Ellicott Commentary Genesis 27:33

"And Isaac trembled very exceedingly, and said, Who then is he that hath taken venison, and brought it me, and I have eaten of all before thou camest, and have blessed him? Yea, [and] he shall be blessed." — Genesis 27:33 (ASV)

Isaac trembled very exceedingly. —This was not from mere vexation at having been so deceived and made to give the blessing contrary to his wishes. What Isaac felt was that he had been resisting God. In spite of the prophecy given to the mother, and Esau’s own irreligious character and heathen marriages, he had determined to bestow on him the birthright by an act of his own will; and he had failed.

But he persists no longer in his sin. Acknowledging the Divine purpose, he has no word of blame for Rebekah and Jacob, but confirms to him the possession of the birthright, and declares, Yea, he shall be blessed.