Esau said, “Is he not rightly named Jacob? For he has supplanted me these two times. He took away my birthright, and look, now he has taken away my blessing.” Then he said, “Have you not reserved a blessing for me?”
The sons of Reuben the firstborn of Israel. (He was the firstborn, but because he defiled his father’s bed his birthright was given to the sons of Joseph son of Israel, so that he is not enrolled in the genealogy according to the birthright;
then on the day when he wills his possessions to his sons, he is not permitted to treat the son of the loved as the firstborn in preference to the son of the disliked, who is the firstborn.
He must acknowledge as firstborn the son of the one who is disliked, giving him a double portion of all that he has; since he is the first issue of his virility, the right of the firstborn is his.