Genesis 25:31

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 כיום "juxta hunc diem", Fagius, Drusius.