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 (Numbers 3:12,13; 8:18).
The first-born inherited the judicial authority of his father, whatever it might be (2 Chronicles 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 (Romans 8:29; Colossians 1:18; Hebrews 1:4-6). As first-born he has an inheritance superior to his brethren, and is the alone true priest.