Devarim 21,17: but he shall acknowledge the first-born, the son of the hated, by giving him a double portion of all that he hath; for he is the first-fruits of his strength, the right of the first-born is his.
What makes the firstborn so special that he receives a double portion? Many commentaries have offered explanations, but ultimately the halachah is derived from the verse itself. (As you’ll see below, some of the reasons would apply equally to firstborn daughters, or to the mother’s firstborn. Yet the halachic firstborn is the father’s oldest son.)
Beloved by G-d
“All firsts are beloved by G-d.” Just as there is the mitzvah that the first fruits are brought as an offering to G-d (bikkurim), as is the first of the flock (bechor beheimah), so does G-d have a special love for the firstborns, and they are given a double portion. (Abarbanel, Devarim 21,15)
In the Father’s Stead
It is the firstborn who stands in the father’s stead, perpetuating his continued memory. It was his birth that made the father into a father, revealing his latent power of parenthood. (Abarbanel, ibid.)
Although further elaboration is beyond the scope of this article, this is one of the reasons given as to why it was generally only the sons who inherited, as in ancient times it was the sons who would carry on the family name. Property ownership was generally passed down through the males, and they in turn were obligated to support their unmarried sisters (that is, unless there were no sons, in which case the daughters inherited, as in the fascinating incident of the five righteous daughters of Tzelafchad). However, as we’ll discuss later, there is a way to include the daughters in the inheritance as well.
In the Levites’ Stead
Originally, the firstborns were supposed to dedicate their lives to the Divine service in the Temple. Due to their part in the sin of the Golden Calf, the Temple service was taken away from them and given to the Levites, who don’t get a portion in the land. In their stead, the firstborns get a double portion, theirs and the Levites. Had the firstborn remained obligated in the Temple, they too would not have been granted an inheritance. Now however, that they were replaced, they not only receive their own portion of their father’s estate, but they receive an extra one – in place of the one lost by Levi. (Chizkuni, Bemidbar 3,12)
Paving the Way
The first child born from the mother’s womb paves the way for all subsequent children. The double portion is an expression of gratitude. (Midrash Talpiot, s.v. Bechor.)
Takes over the Family’s Affairs
The oldest son would naturally take over the family’s affairs with the father’s passing. It was thus natural to give him a larger portion of the family estate. The firstborn is also credited with making his father into a father; thus, he has a special role in the family (R. Samson Raphael Hirsh Devarim 21,17).
Example of the double portion for the First-Born:
If the Father leaves behind four sons, the inheritance is divided into five portions.
Reuven (2 portions) Shimon (1) Levi (1) Yehudah (1)
