This term denotes the rights or privileges belonging to the first-born among the Hebrews. The particular advantages which these conferred were the following—
1. A right to the priesthood. The first-born became the priest in virtue of his priority of descent, provided no blemish or defect attached to him. Reuben was the first-born of the twelve patriarchs, and therefore the honor of the priesthood belonged to his tribe. God, however, transferred it from the tribe of Reuben to that of Levi (Numbers 3:12-13; Numbers 8:18). Hence the first-born of the other tribes were redeemed from serving God as priests, by a sum not exceeding five shekels. Being presented before the Lord in the temple, they were redeemed immediately after the thirtieth day from their birth (Numbers 18:15-16; Luke 2:22). It is to be observed, that only the first-born who were fit for the priesthood (i.e. such as had no defect, spot, or blemish) were thus presented to the priest.
2. The first-born received a double portion of his father's property. There is some difficulty in determining precisely what is meant by a double portion. Some suppose that half the inheritance was received by the elder brother, and that the other half was equally divided among the remaining brethren. This is not probable. The Rabbins believe that the elder brother received twice as much as any of the rest: and there is no reason to doubt the correctness of this opinion. When the first-born died before his father's property was divided, and left children, the right of the father descended to the children, and not to the brother next of age.
3. He succeeded to the official authority possessed by his father. If the latter was a king, the former was regarded as his legitimate successor, unless some unusual event or arrangement interfered.
After the law was given through Moses, the right of primogeniture could not be transferred from the first-born to a younger child at the father's option. In the patriarchal age, however, it was in the power of the parent thus to convey it from the eldest to another child (Deuteronomy 21:15-17; Genesis 25:31-32).
It is not difficult to perceive the reason why the first-born enjoyed greater privileges than the rest of the children. The peculiar honor attaching to them is easily accounted for. They are to be viewed as having reference to the Redeemer, the first-born of the Virgin. Hence in the Epistle to the Romans (Romans 8:29), it is written concerning the Son, 'that he might be the firstborn among many brethren;' and in Colossians 1:18, 'who is the beginning, the first-born from the dead; that in all things he might have the preeminence' (see also Hebrews 1:4-6) As the firstborn had a double portion, so the Lord Jesus, as Mediator, has an inheritance superior to His brethren; He is exalted to the right hand of the Majesty on high, where He reigns until all His enemies shall be subdued. The universe is His rightful dominion in his mediatorial character. Again, He alone is a true priest: He fulfilled all the functions of the sacerdotal office; and the Levites, to whom, under the law, the priesthood was transferred from all the first-born of Israel, derived the efficacy of their ministrations from their connection with the great high-priest.