Why was the double portion of Isaac's wealth so significant?

Les explains that the birthright itself did not create the enmity between Jacob and Esau; the blessing did, because the blessing was the material side of the whole picture. The material blessing said the eldest son would get a double portion. If there were three sons, the father would divide the estate into four parts—the oldest getting two parts and the others each one. In Isaac's case with two sons, the estate would be divided into three parts, the eldest getting two and the other one. Esau was interested in that; he was not about to give up that double portion, and that is why he got so upset when he found out that the blessing had already been given to Jacob. That meant Jacob was now in the line of the Messiah, which meant nothing to Esau, but also that Jacob would get a double portion of the wealth of his father Isaac. These people were wealthy for their time and day, having flocks and herds and servants, and even Abraham had a good collection of gold and silver.