You can find the answer in the JFB commentary, which I have included below:
Jacob said, Sell me . . . thy birthright--that is, the rights and privileges of the first-born, which were very important, the chief being that they were the family priests [Ex 4:22] and had a double portion of the inheritance [De 21:17].
We can see from this story that Esau took lightly the inheritance that was his from his birthright and was willing to sell his inheritance for a bowl of soup. Sometimes, we do that too ... we know that we have inherited blessings and much more from God, but we let our stomach, our emotions, or our lusts get the better of us and we give up our inheritance for pleasures which do not last forever.