Esau was cheated by his brother, or Jacob bested his brother in a quick bargain. It is a matter of perspective. Esau gave up something valuable for something very minor. Esau was hungry NOW and wanted to eat. ‘Mess of pottage’, has come to mean: something considered of little value. The phrase is colorful, and evocative. It is one of many turns of biblical phrase that lingers in the idiom and vernacular.
Genesis xxv. 29-34.Mess refers broadly to food: its amount, softness, mixture, companions at table, and location of table. Pottage is a soft, semiliquid food; a simple, boiled stew.
And Jacob boiled pottage: to whom Esau, coming faint out of the field, Said: Give me of this red pottage, for I am exceeding faint. For which reason his name was called Edom. And Jacob said to him: Sell me thy first birthright. He answered: Lo I die, what will the first birthright avail me. Jacob said: Swear therefore to me. Esau swore to him, and sold his first birthright. And so taking bread and the pottage of lentils, he ate, and drank, and went his way; making little account of having sold his first birthright. ―DRC
Coxit autem Jacob pulméntum : ad quem cum venísset Ésau de agro lassus, ait : Da mihi de coctióne hac rufa, quia óppido lassus sum. Quam ob causam vocátum est nomen ejus Edom. Cui dixit Jacob : Vende mihi primogénita tua. Ille respóndit : En mórior, quid mihi próderunt primogénita ? Ait Jacob : Jura ergo mihi. Jurávit ei Ésau et véndidit primogénita. Et sic, accépto pane et lentis edúlio, comédit et bibit, et ábiit, parvipéndens quod primogénita vendidísset.
And Jacob sod pottage: and Esau came from the field, and he was faint: And Esau said to Jacob, Feed me, I pray thee, with that same red pottage; for I am faint: therefore was his name called Edom. And Jacob said, Sell me this day thy birthright. And Esau said, Behold, I am at the point to die: and what profit shall this birthright do to me? And Jacob said, Swear to me this day; and he sware unto him: and he sold his birthright unto Jacob. Then Jacob gave Esau bread and pottage of lentiles; and he did eat and drink, and rose up, and went his way: thus Esau despised his birthright. ―KJV
Now, in the english, ‘pottage’ is used thrice. In the latin: pulmentum (appetizer) is used first, coctióne hac rufa (this red cooking) next, and finally, pane et lentis edúlio (bread and lentil edible). Pottage is not much used to-day in english, potage is in french.