First son born to a couple and required of newly married people was believed to represent the prime of human vigor (Gen 49:3; Ps 78:51). In memory of the death of Egypt’s firstborn and the preservation of the firstborn of Israel, all the firstborn of Israel, both of man and beast, belonged to Yahweh (Exod 13:2,15; cp. 12:12-16). This meant that the people of Israel attached unusual value to the eldest son and assigned special privileges and responsibilities to him.
He was presented to the Lord when he was a month old. Since he belonged to the Lord, it was necessary for the father to buy back the child from the priest at a redemption price not to exceed five shekels (Num 18:16). The husband of several wives would have to redeem the firstborn of each.
The birthright of a firstborn included a double portion of the estate and leadership of the family. As head of the house after his father’s death, the eldest son customarily cared for his mother until her death, and he also provided for his sisters until their marriage. The firstborn might sell his rights as Esau did (Gen 25:29-34) or forfeit them for misconduct as Reuben did because of incest (Gen 35:22; 49:3-4).
The firstborn of a clean animal was brought into the sanctuary on the eight day after birth (Exod 22:29-30). If it were without blemish, It was sacrificed (Deut 15:19; Num 18:17). If if had a blemish, the priest to whom it was given could eat it as common food outside Jerusalem (Deut 15:21-23), or it could be eaten a home by its owner. Apparently the firstborn of a clean animal was not to be used for any work since it belonged to the Lord (Deut 15:19). END OF PART 1