Matthew Henry on Genesis 27:18-29

Jacob, with some difficulty, gained his point, and got the blessing. This blessing is in very general terms. No mention is made of the distinguishing mercies in the covenant with Abraham. This might be owing to Isaac having Esau in his mind, though it was Jacob who was before him. He could not be ignorant how Esau had despised the best things. Moreover, his attachment to Esau, so as to disregard the mind of God, must have greatly weakened his own faith in these things. It might therefore be expected, that leanness would attend his blessing, agreeing with the state of his mind.