"Once when Jacob was cooking some stew, Esau came in from the open country, famished. He said to Jacob, 'Quick, let me have some of that red stew! I'm famished!' (That is why he was also called Edom.)" NIV translation
We see that Esau was a man of the flesh as, when he saw some stew, he just had to have it then and now. He would not have been that hungry as he was a child in Abraham's family and they were well off.
"Jacob replied, 'First sell me your birthright.' 'Look, I am about to die,' Esau said. 'What good is the birthright to me?' But Jacob said, 'Swear to me first.' So he swore an oath to him, selling his birthright to Jacob." NIV translation
Jacob immediately asked for Esau's rights as the firstborn son in return for a bowl of soup. Surely, Rebekah had told him about what God had said concerning the older serving the younger. Instead of waiting on God to fulfill His word, Jacob took matters into his own hands.
We all must admit that, at times, we try to do the same thing as we get impatient. We must remember that God has always kept His promises and His timing is perfect.
"Then Jacob gave Esau some bread and some lentil stew. He ate and drank, and then got up and left. So Esau despised his birthright." NIV translation
This birthright included the majority of the family wealth but also at the heart of it were the promises that God had made to Abraham. With these rights came responsibility for the spiritual health of the family. Esau, being a man of the flesh, did not care about spiritual matters and didn't want the responsibility of being the family priest. He cared so little about the things of God that he thought that a little bread and soup were worth more.
This struggle between the physical and the spiritual is something that we all must face.