Bible Dictionary
Firstborn
The firstborn, especially the eldest son, held a privileged place in the family and ordinarily received a double portion of the inheritance. Under the law, Israelite firstborn sons and male animals were devoted to God and subject to redemption or offering.
Biblical Usage
The eldest son was redeemed by an offering of no more than five shekels within one month of birth. Under the monarchy he usually succeeded his father, though this was not always so. Unclean animals were redeemed, sold, or put to death according to the law.
Scripture References