He must acknowledge the son of his unloved wife as the firstborn by giving him a double share of all he has. That son is the first sign of his father's strength. The right of the firstborn belongs to him.
""Reuben, you are my firstborn, my might, the first sign of my strength, excelling in honor, excelling in power." -
"when he wills his property to his sons, he must not give the rights of the firstborn to the son of the wife he loves in preference to his actual firstborn, the son of the wife he does not love." -
"A man is not to marry his father's wife; he must not dishonor his father's bed." -
"The first offspring of every womb, both man and animal, that is offered to the LORD is yours. But you must redeem every firstborn son and every firstborn male of unclean animals." -