Еврейская мысль к Берешит 25:34

It is then related that Jacob gave the bread and the pottage to Esau, who reveled in the filling of his belly and shamed the birthright. Even after he had gone he did not regret his folly and his wickedness and say: "What have I done!" This is the intent of (Genesis 25:34): "And he ate, and he drank, and he arose, and he went away, and he shamed…" That is, even after he went away. Indeed, we never find him regretting the act at all, except in conjunction with his complaint over losing the blessing, as it is written (Ibid 27:36): "He took my birthright, and now he has taken my blessing." It is only when he has a mundane complaint that he spills out everything along with it. In addition to this, he realized then that the tie between Isaac and his children was an extremely valuable commodity, "for His blessed ones shall inherit the land" (Psalms 37:22). It is for this reason that he worried about the birthright. Add to this the fact that at the time he was more than sixty years old, whereas his shaming of the birthright had taken place when he was a callow youth of fifteen, for which reason he made light of it and sold it for a mess of lentils (or received full payment for it, though this is not stated explicitly, according to those who subscribe to this view).