Musar sur La Genèse 27:13

A third problem is how we are to understand Rebeccah who said to her son Jacob: "May your curse be on my head, my son!" Could she imagine that Jacob would make peace with the idea that his mother would be cursed through something he did?

Esau is characterized as "descending;" this is alluded to in Ovadiah 1,4, where the prophet says to Edom: "Even if you place your nest among the stars, I shall bring you down from there." When Rebeccah said; "your curse upon me, my son," she referred to what had already occurred in her womb before the twins were born, i.e. that everything that is accursed was already concentrated in Esau. He, Jacob, did not have to worry, seeing he was already blessed.