In Chapter 25:29-34, we read where Esau gave away his birthright in exchange for a bowl of stew, and even without knowing exactly what a birthright is, we can reasonably infer that this was probably an extremely lopsided and uneven exchange. Chapter 27 describes the events of how Jacob came to receive Isaac's blessing, which leads to today's question:
What is the difference between a blessing and a birthright?
In the days of yore, the birthright was what we consider to be the estate or inheritance of today, and the eldest son was given a double portion. For example, if there were two sons, one son would receive 2/3rds and the second 1/3, if there were three, it would be 1/2, 1/4, and 1/4 and so on. This custom was long and persistent, eventually evolving into other traditions (first son got the land, second goes into the military, third to the clergy, fourth, well, uh...). The impetus for many an immigrant to America is grounded in these traditions, since a son without backing would need to find new territory in which to establish himself.
With no proof to the contrary, we can assume that Esau was fully aware that he had forfeited his birthright. Any discussion on this topic is best accomplished with an amber-colored beverage in my hand, since we'll never know. Given that, the blessing that Esau sought from Isaac was different. The blessing was the designation of whom was the head of the extended family upon the death of the father. Being no scholar, I can't explicitly explain what the difference between this honorary designation vs. the economic one of the birthright is, since I can't readily explain what it means to be the "head of the household." Honor is one thing, but it won't pay the bills. Granted, in most cases, it didn't matter--again, the eldest usually received the blessing as well.
I try not to psychoanalyze removed 4,000 years from the person, but it would appear that Esau was attempting to establish his place in the family after Isaac was gone. He could have been thinking that since his wealth was primarily in livestock, they could reproduce and he could be as rich as Jacob, and still have the blessing and not lose anything in the bargain. We're going to learn in the upcoming chapters that Jacob had his moments where he was more than willing to bend the rules to get what he wanted, but don't pity Esau at this point either. We read earlier that Isaac was 60 when Jacob and Esau were born, and will read later he lived to 180, so Esau certainly had plenty of time to understand how Jacob lived. We will come to see that most of the enemies of Israel in the later years will be descended from Esau. They started fighting in the womb and basically spent their entire lives doing the same thing, setting the stage for a long and glorious Old Testament history filled with war between nations that were related by blood.