Birthright

This word denotes the special privileges and advantages belonging to the first-born son among the Jews. He became the priest of the family. Thus Reuben was the first-born of the patriarchs, and so the priesthood of the tribes belonged to him. That honour was, however, transferred by God from Reuben to Levi (Num 3:12, 13; 8:18).
The first-born son had allotted to him also a double portion of the paternal inheritance (Deut 21:15-17). Reuben was, because of his undutiful conduct, deprived of his birth-right (Gen 49:4; 1Chr 5:1). Esau transferred his birth-right to Jacob (Gen 25:33).
The first-born inherited the judicial authority of his father, whatever it might be (2Chr 21:3). By divine appointment, however, David excluded Adonijah in favour of Solomon.
The Jews attached a sacred importance to the rank of "first-born" and "first-begotten" as applied to the Messiah (Rom 8:29; Col 1:18; Heb 1:4-6). As first-born he has an inheritance superior to his brethren, and is the alone true priest.