day. Figure of speech Brachyology. App-6. Supply "that thou wilt sell it".
birthright. The Severus Codex here reads "ware", i.e. Esau treated his birthright as merchandise. See App-34.
Related Commentaries of Genesis 25:33
Genesis 25:33
33 And Jacob said, Swear to me this day; and he sware unto him: and he sold his birthright unto Jacob.