Sell me this day thy birthright - What the בחרה bechorah or birthright was, has greatly divided both ancient and modern commentators. It is generally supposed that the following rights were attached to the primogeniture:
1. Authority and superiority over the rest of the family.
2. A double portion of the paternal inheritance.
3. The peculiar benediction of the father.
4. The priesthood, previous to its establishment in the family of Aaron.
Calmet controverts most of these rights, and with apparent reason, and seems to think that the double portion of the paternal inheritance was the only incontestable right which the first-born possessed; the others were such as were rather conceded to the first-born, than fixed by any law in the family. However this may be, it appears,
1. That the first-born were peculiarly consecrated to God, Exodus 22:29.
2. Were next in honor to their parents, Genesis 49:3.
3. Had a double portion of their father's goods, Deuteronomy 21:17.
4. Succeeded him in the government of the family or kingdom, 2-Chronicles 21:3.
5. Had the sole right of conducting the service of God, both at the tabernacle and temple; and hence the tribe of Levi, which was taken in lieu of the first-born, had the sole right of administration in the service of God, Numbers 8:14-18; and hence we may presume, had originally a right to the priesthood previous to the giving of the law; but however this might have been, afterwards the priesthood is never reckoned among the privileges of the first-born.
That the birthright was a matter of very great importance, there can be no room to doubt; and that it was a transferable property, the transaction here sufficiently proves.

And Jacob said, sell me this day thy birthright. Which had many privileges annexed to it, as honour and authority in the family next to parents; a double portion of inheritance; some say the exercise of priesthood, but that is questioned; the parental blessing, and especially in this the promises of the Messiah, and of inheritance of the land of Canaan, and which was typical of the heavenly inheritance: all which Rebekah knew by the divine oracle were designed for Jacob, and which no doubt she had acquainted him with, and advised him to deal with his brother about parting with his birthright as he had opportunity; and very likely they had talked together about it before in a distant manner, and Esau had shown some indifference to his right, and made no great account of it; and now, an opportunity offering to get him in the mind to part with it, he takes it, and moves for a sale of it immediately, at once, without any more delay, and even before he had his pottage; thus taking the advantage of his brother's necessity: or, sell it me "as the day" (x), let the bargain be as clear as the day, as Jarchi interprets it; let it be made in plain and full terms, that there may be no dispute about it hereafter, or any revocation of it: but the former sense seems best, as appears from Genesis 25:33, where the same way of speaking is used.
(x) "juxta hunc diem", Fagius, Drusius.

Jacob said, Sell me . . . thy birthright--that is, the rights and privileges of the first-born, which were very important, the chief being that they were the family priests (Exodus 4:22) and had a double portion of the inheritance (Deuteronomy 21:17).

Sell me this day thy birth - right - He cannot be excused in taking advantage of Esau's necessity, yet neither can Esau be excused who is profane, Hebrews 12:16, because for one morsel of meat he sold his birth - right. The birth - right was typical of spiritual privileges, those of the church of the first - born: Esau was now tried how he would value those, and he shews himself sensible only of present grievances: may he but get relief against them, he cares not for his birth - right. If we look on Esau's birth - right as only a temporal advantage, what he said had something of truth in it, that our worldly enjoyments, even those we are most fond of, will stand us in no stead in a dying hour. They will not put by the stroke of death, nor ease the pangs, nor remove the sting. But being of a spiritual nature, his undervaluing it, was the greatest profaneness imaginable. It is egregious folly to part with our interest in God, and Christ, and heaven, for the riches, honours, and pleasures of this world.