the birthright: the special standing and rights that belonged to the firstborn son.
In ancient Israel the oldest son held a privileged place, and this word names that place itself, not the son. It is the abstract word that stands behind the ordinary word (בכור) for a firstborn person. Where one word means "the firstborn son," this word means "what it is to be that son": his rank in the family and the advantages that came with it.
Those advantages were a bundle.
- The firstborn received a larger share of the inheritance, often described as a double portion.
- He became head of the household when the father died.
- He held a claim on the father's formal blessing.
- And there was a sacred side to it as well, since the firstborn of every Israelite family was regarded as belonging in a special way to God.
So the birthright was at once a matter of property, of leadership, and of standing before God.
The striking thing in the Bible is how often this birthright changes hands. Esau trades his away for a bowl of stew and is said to have despised it. Reuben forfeits his through sin, and it passes to Joseph's line. Again and again the expected order of the oldest son is overturned. That pattern is the point: the writers use this word to show that the highest place in the family, and by extension the chosen place among the nations, is something given rather than simply owed by birth.
Most of the time the word points to that whole package of privilege. In one passage it leans instead on the plain idea of seniority, the rank of who was born first, when Joseph seats his brothers from oldest to youngest. The core is the same either way: the standing that goes with being the firstborn.