In Middle Eastern custom, which twin received the inheritance rights?
In Middle Eastern custom, the twin born first held the status of eldest son and was the rightful heir of the inheritance. That standard applied even to twins, so the firstborn twin received the inheritance rights, contrary to the election where the elder would serve the younger.
Les explains that this was contrary to Middle Eastern custom. Even in the case of twins, whichever twin was born first would be the eldest son and the rightful heir of the inheritance. Les notes this flew in the face of what Isaac and Rebekah understood, because God said the younger, second twin Jacob, would be the ascendant one and the one through whom the promises would come. Les sees this as against human reason, but God in His foreknowledge, before those lads were ever born, knew that Esau would be destitute of faith.