Charles Spurgeon Commentary Genesis 27:21-29

"And Isaac said unto Jacob, Come near, I pray thee, that I may feel thee, my son, whether thou be my very son Esau or not. And Jacob went near unto Isaac his father. And he felt him, and said, The voice is Jacob`s voice, but the hands are the hands of Esau. And he discerned him not, because his hands were hairy, as his brother Esau`s hands. So he blessed him. And he said, Art thou my very son Esau? And he said, I am. And he said, Bring it near to me, and I will eat of my son`s venison, that my soul may bless thee. And he brought it near to him, and he did eat. And he brought him wine, and he drank. And his father Isaac said unto him, Come near now, and kiss me, my son. And he came near, and kissed him. And he smelled the smell of his raiment, and blessed him, and said, See, the smell of my son Is as the smell of a field which Jehovah hath blessed. And God five thee of the dew of heaven, And of the fatness of the earth, And plenty of grain and new wine. Let peoples serve thee, And nations bow down to thee. Be lord over thy brethren, And let thy mother`s sons bow down to thee. Cursed be every one that curseth thee, And blessed be every one that blesseth thee." — Genesis 27:21-29 (ASV)

And Isaac said to Jacob, Come near, please, that I may feel you, my son, whether you are my very son Esau or not.

And Jacob went near to Isaac his father; and he felt him, and said, The voice is Jacob's voice, but the hands are the hands of Esau. And he did not discern him, because his hands were hairy, as his brother Esau's hands: so he blessed him. And he said, Are you my very son Esau? And he said, I am. And he said, Bring it near to me, and I will eat of my son's venison, that my soul may bless you.

And he brought it near to him, and he ate: and he brought him wine, and he drank. And his father Isaac said to him, Come near now, and kiss me, my son. And he came near, and kissed him: and he smelled the scent of his clothing, and blessed him, and said, See, the smell of my son is as the smell of a field which the Lord has blessed: therefore God give you of the dew of heaven, and the fatness of the earth, and plenty of grain and wine: Let people serve you, and nations bow down to you: be lord over your brothers, and let your mother's sons bow down to you: cursed be every one that curses you, and blessed be he that blesses you.

So he tied his own hands: he could not revoke his blessing, or, had he done so, he would have brought the curse upon himself.