Why did Esau sell his birthright for a bowl of stew?

Because, in the narrator's own editorial judgment, he despised it.

The scene is Genesis 25:29–34. Esau comes in from hunting, starving. Jacob is cooking lentil stew. Esau demands the food. Jacob names a price: "Sell me today your birthright (בְּכוֹרָה, bekhorah, H1062)."

Esau's reply is the giveaway: "I am about to die; of what use is a birthright to me?" (Gen 25:32). He trades the thing for the stew. And then the narrator closes the scene with a single verb:

וַיִּ֥בֶז עֵשָׂ֖ו אֶת־הַבְּכֹרָֽה

va-yivez Esav et-ha-bekhorah

"And Esau despised the birthright." — Genesis 25:34b

The Hebrew verb va-yivez comes from the root בזה (H959), meaning "to despise, to hold in contempt, to treat as worthless." It's the same root that appears in Proverbs 15:20 ("a foolish man despises his mother") and in the Servant Song of Isaiah 53:3 ("he was despised and rejected"). The word is strong. The narrator is not saying Esau was impulsive or hungry or unlucky. He is saying Esau treated a sacred thing as worthless.

What was the bekhorah? In the Torah's own law — given centuries later by Moses but valid as theological category all along — the firstborn received a double portion of inheritance (Deut 21:17), was consecrated to the LORD (Exo 13:2), and stood in a priestly function that the tribe of Levi later absorbed on behalf of the nation (Num 3:11–13). It wasn't just a legal privilege. It was the family's covenantal future — the line through which the promises to Abraham and Isaac would run. Esau was Isaac's firstborn. He traded the covenantal line for a hot meal.

The New Testament's only explicit exegesis of the birthright concept comes in Hebrews 12:16, and it reads the scene exactly this way:

"Let no one be sexually immoral or godless (βέβηλος) like Esau, who sold his own birthright (πρωτοτόκια) for a single meal." — Hebrews 12:16

The Greek word βέβηλος (bebēlos, G0952) means "profane, unhallowed" — the opposite of hagios, "holy." Hebrews is not saying Esau was irreligious in the modern sense. It is saying Esau treated holy things as common. That is the shape of his sin. He had the sacred inheritance; he traded it for appetite.

Hebrews then adds the pastoral application: "For you know that afterward, when he desired to inherit the blessing, he was rejected. For he found no chance to repent, though he sought it with tears" (Heb 12:17). The warning is for the first-century church under persecution: do not do what Esau did. Do not trade what God has given you for immediate relief.

This is why Esau stands in Hebrews as the NT's one named warning example for what the birthright was and what it cost to throw it away. Jacob, for all his complicated history, desired the covenantal thing. Esau, for all his strength as the elder, did not.

The Hebrew verb va-yivez carries the whole theological weight. Esau was not tricked out of his birthright. He despised it. The text is uncompromising on that point, and the NT preserves the judgment.

For the full treatment — including the six-pair reversal pattern of which Esau/Jacob is one instance, and the πρωτότοκος Christology that completes it — see the study The Firstborn.