Why did the blessing cause enmity between Jacob and Esau when the birthright did not?

Les explains that the birthright did not create the enmity that the blessing did. From the time the brothers were 24 until they were 77, there was no enmity between them; if they had contact, they evidently got along. The blessing, however, was the material side of the whole picture. The material blessing meant the eldest son would receive a double portion of the estate. If there were three sons, the father would divide the estate into four parts: the oldest would get two, and the others one each. Here the estate would be divided into three parts, with the eldest getting two and the other one. Esau was interested in that and was not about to give up that double portion. That is why he got so uptight when he found out the blessing had already been given to Jacob. The blessing also meant Jacob was now in the line of the Messiah, which meant nothing to Esau, but it also meant Jacob would get a double portion of the wealth of his father Isaac. These people were wealthy for their time, with flocks, herds, and servants; even old Abraham had a pretty good collection of gold and silver.