Genesis 27:33

And Isaac trembled very exceedingly, and said, Who? Where 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. Esau's simple statement, so obviously the truth, caused the greatest agitation in Isaac's manner; literally, he trembled a great trembling very exceedingly, and then broke out into various questions as to the identity of the person who had so cleverly obtained the chief blessing from him. But even before Isaac pronounces the name of Jacob, he must state that the blessing of the Lord will remain with him. It was not for him to withdraw the blessing which was in fact that of the Lord, and Isaac now realized that his fleshly preference for Esau could not be defended in the sight of God. No matter in what manner the blessing had been obtained, God had guided the affair so that Jacob now actually was the bearer of the patriarchal succession.